HydrologyAndy Bullock and and Earth Mike System Acreman Sciences, 7(3), 358–389 (2003) © EGU

The role of wetlands in the hydrological cycle

Andy Bullock1 and Mike Acreman2

1Independent Consultant, Ledbury, Herefordshire, HR8 2DX, UK 2Centre for Ecology and Hydrology, Wallingford, Oxon. OX10 8BB, UK.

Email for corresponding author: [email protected]

Abstract It is widely accepted that wetlands have a significant influence on the hydrological cycle. Wetlands have therefore become important elements in water management policy at national, regional and international level. There are many examples where wetlands reduce floods, recharge groundwater or augment low flows. Less recognised are the many examples where wetlands increase floods, act as a barrier to recharge, or reduce low flows. This paper presents a database of 439 published statements on the water quantity functions of wetlands from 169 studies worldwide. This establishes a benchmark of the aggregated knowledge of wetland influences upon downstream river flows and groundwater aquifers. Emphasis is placed on hydrological functions relating to gross water balance, groundwater recharge, base flow and low flows, flood response and river flow variability. The functional statements are structured according to wetland hydrological type and the manner in which functional conclusions have been drawn. A synthesis of functional statements establishes the balance of scientific evidence for particular hydrological measures. The evidence reveals strong concurrence for some hydrological measures for certain wetland types. For other hydrological measures, there is diversity of functions for apparently similar wetlands. The balance of scientific evidence that emerges gives only limited support to the generalised model of flood control, recharge promotion and flow maintenance by wetlands portrayed throughout the 1990s as one component of the basis for wetland policy formulation. That support is confined largely to floodplain wetlands, while many other wetland types perform alternate functions — partly or fully. This paper provides the first step towards a more scientifically defensible functional assessment system.

Keywords: wetlands, hydrological functions, flood reduction, groundwater recharge, low flows, evaporation

Introduction Kusler and Riexinger (1985) reported that “the science base Open any book on wetland conservation and it will and efforts to assimilate existing studies are still inadequate encourage the maintenance of wetlands partly because of with regard to some functions, particularly hydrology”. their role in the water cycle. Wetlands are said to perform The basic references on the hydrological functions of “hydrological functions”; to “act like a sponge”, soaking- wetlands are summaries of studies collated in the USA in up water during wet periods and releasing it during dry the 1980s (Adamus and Stockwell, 1983; Bardecki, 1984; periods (eg. Bucher et al., 1993). As Maltby (1991) reports Carter, 1986). These summaries have been used by “ the case for wetland conservation is made in terms of organisations, such as IUCN-The World Conservation Union ecosystem functioning, which result in a wide range of (Dugan, 1990), Wetlands International (Davis and Claridge, values including groundwater recharge and discharge, flood 1993) and the Ramsar Convention on Wetlands of flow alteration, sediment stabilization, water quality ..”. International Importance (Davis, 1993). They have Since wetlands cover around 6% of the land surface of the influenced international wetland policy (OECD, 1996) and earth (OECD, 1996) and many exist in the upstream parts its uptake at the national (eg. Zimbabwe and Uganda), and of river catchments, the total downstream area over which continental levels e.g. Europe (CEC, 1995) and Asia (Howe a hydrological influence may be exerted is substantial. Yet et al., 1992). the hydrological processes and behaviour of wetland Recent emphasis at the Second World Water Forum in ecosystems has certainly lacked the scientific integration The Hague 2000 and the World Summit on Sustainable received by other land surface systems, such as forests. Development 2002 in Johannesburg was placed on the need

358 The role of wetlands in the hydrological cycle

to ensure the integrity of ecosystems as part of integrated l the review is restricted to freshwater wetlands, water resources management. Also receiving high excluding lakes; prominence was the use of water to meet basic human needs l conclusions of wetland function must be supported by and economic development. Thus, it is essential to re- hydrological data and not based on the original author’s examine, periodically, the conclusions of scientific studies opinion alone; on wetland functions. This ensures that policy at all levels l double-accounting is avoided, whereby repetition of is underpinned by a consensus of sound scientific opinion. conclusions for an individual wetland in successive The scientific literature contains a range of studies that publications is not duplicated; describe the water quantity functions of individual or groups l unsubstantiated generic statements, such as wetlands of wetlands. They represent a substantial accumulation of reduce flooding, are not included. hydrological knowledge. The majority of these papers supports the notion that wetlands have a significant influence Consistency is ensured by extracting common elements from on the hydrological cycle. However, many recognise that the diverse sources. Important information is maintained in “it is difficult to make definitive statements regarding the the detail of the particular hydrological function, wetland role of various types of wetlands in runoff production or type and the manner of conclusion. The approach adopted storm water detention” (Carter, 1986). Furthermore, some was to complete the following general statement (where studies have produced evidence that contradicts previous bracketed and underlined phrases relate to elements in widely accepted knowledge. For example, the classic Annex 1) for each study: hydrological studies of Hewlett and Hibbert (1967) “(Author(s)) undertook a study in a given location identified headwater wetlands along river margins as flood (country, or US State/Canadian Province or Territories) of generating areas. Burt (1995) concluded that “ most a particular hydrological type of wetland (wetland type), wetlands make very poor aquifers; ... accordingly, they yield also referred to by a more general or locally-specific wetland little base flow, but in contrast, generate large quantities of term (local term). Based on results from a particular type flood runoff. Far from regulating river flow, wetlands usually of study (categorisation of wetland study) and drawing provide a very flashy runoff regime”. inferences in a particular manner (basis of inference), the This paper has three objectives: first, to present an ordered authors conclude (page number) that the wetland performs database of published papers on hydrological functions of a particular function with respect to a specific hydrological wetlands; second, to provide a collation of scientific measure (hydrological measure), as can be summarised evidence among hydrological measures and wetland type; by a functional statement (summary functional statement) third, to stimulate debate and further research. The focus of and a summary function (summary of wetland water this paper is limited to water quantity functions, including quantity function)”. impacts on water resource availability, groundwater There are, therefore, ten elements extracted from each replenishment and flood control. It does not consider other publication, each entered into the database. Explanation of aspects of wetlands, such as water quality or biodiversity, each of these elements is expanded upon below. Because which are part of a wider case for wetland conservation. the format of the review is tabular, abbreviated codes are adopted for some elements for purposes of brevity.

Creating a literature-based review of Author(s): Citation to original source. water quantity functions With the objective of creating a comprehensive and Country, or US State/Canadian Province or Territories: consistent database of past studies, a literature review of Location of wetland study. water quantity functions was undertaken by keyword searches on the major databases of abstracts, and by tracking Wetland type: For the purpose of this study, wetlands are citations to earlier and related studies. Consequently, the categorised into five types according to three broad database is drawn from 169 publications that report the hydrological features (Table 1), based, with modification, results of scientific study that quantify hydrological upon the scheme proposed by Novitski (1978) for Wisconsin functions of wetlands. Papers that report other authors’ wetlands and subsequently applied by Adamus and findings or give only qualitative descriptions of wetland Stockwell (1983). The three hydrological features are process are not included. general catchment location, connectivity with the Certain guidelines were followed, namely that: groundwater system and connectivity with the downstream channel network. General catchment location distinguishes

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Table 1. Categorisation of wetland type by hydrological features

Type Wetland type Code Features

HEADWATER Surface water depression SW/D No hydraulic connectivity with groundwater. Outlet has no direct connectivity with river system Surface water slope SW/S No hydraulic connectivity with groundwater. Outlet has direct connectivity with river system Groundwater depression GW/D Hydraulic connectivity (permanent or periodic) with groundwater. Outlet has no direct connectivity with river system Groundwater slope GW/S Hydraulic connectivity (permanent or periodic) with groundwater. Outlet has direct connectivity with river system

FLOODPLAIN Floodplain FP Inputs are dominantly upstream river flows

GENERAL Wetland type, or one element of the type, cannot be specified

between headwater and floodplain; the distinction is that added, and applied where the hydrological context of the headwater wetlands are not fed by significant stream sources. wetland cannot be discerned. Further subdivision applies only to headwater types. The connectivity with the groundwater system distinguishes Local term: Many local terms are applied to wetlands, ‘groundwater’ types that are in hydraulic connectivity with including such general anglicised terms as ‘marsh’, ‘swamp’, the groundwater system for all, or part of, the time, from ‘bog’ etc, and regionally specific terms such as dambo, ‘surface water’ types, which are not. Connectivity with the pakihi, pocosin. There is no known means of providing a downstream channel network distinguishes ‘slope’ types, direct association between local terms and hydrological type which are characterised by an outlet to the downstream river in a fully inclusive manner. system, from ‘depression’ types, which are not. This categorisation deviates from that of Novitski and Adamus Categorisation of wetland study: Wetland studies have and Stockwell by including a floodplain type and in the adopted a number of experimental frameworks, ranging ‘surface–slope’type which, in that scheme, categorises from intensive long-term monitoring of the water balance lakeshore wetlands. Therefore, the two schemes are similar of wetland and non-wetland at the most complex extreme, but are not directly comparable. An unspecified category is to analyses based on single flood event hydrographs. Table 2

Table 2. Categorisation of methodological approach to wetland studies

Category of wetland study Code

Conceptual catchment model CCM Calibration and application of a conceptual catchment model Water balance WB Quantification of the terms of the catchment and/or wetland water balance Long-term hydrograph LTH Analysis of the characteristics of long time series of river flows Single-event hydrograph SEH Analysis of the characteristics of a single river flow event Trend analysis in time series TS Analysis of trends in hydrological time series (associated with detecting the impacts of drainage) Component process COMP Investigation of an individual water balance component or hydrological a process. (See Table 4 for definitions of ‘a’) Chemical balance CHEM Quantification of a chemical process or chemical balance

360 The role of wetlands in the hydrological cycle presents categories of methodological approach with dry season river flows. This kind of conclusion, when taken abbreviated codes for brevity in the tabular review. out of context, leaves unanswered the basis for that conclusion, notably that the wetland reduces (or increases) Basis of inference: Many studies draw conclusions of the river flows — compared with what? Table 3 presents a set kind that, for example, wetlands reduce floods or augment of the comparative scenarios used amongst the various

Table 3. Basis for inference of wetland function

Code Baseline for inference Methodology Limitations

With/out Comparison of the same This approach is restricted to catchment model One case is simulated only. basin, with or without a simulations, in which the model is calibrated in Stability of model parameters. wetland either the “with” or “without” wetland case, as Response of wetland replacement occurs in the modelled catchment. Model runs with zone. the wetland case reversed generate simulated hydrological outputs. Differences between observed and simulated outputs are attributed to the presence of the wetland. Drained Comparison of the same Hydrological outputs from a wetland are observed Response of replacement land-use wetland basin before and prior to drainage. The wetland is drained, and in drained wetland. Initial short- after drainage; or outputs are observed after drainage. Differences in term responses to drainage may neighbouring drained and the pre- and post- drainage outputs are attributed differ from long-term responses. undrained wetlands to the wetland. alternately, outputs from two adjacent catchments, each with wetlands, are observed. One of the catchments is drained, and differences between the outputs between the two catchments are attributed to the presence of the wetland. Pair Comparison of paired Hydrological outputs are observed from two catch- If two catchments are otherwise basins, one with wetland ments, similar in all respects except that one identical, why does only one have the other without that one catchment contains a wetland while the a wetland? second does not. Differences between the outputs are attributed to the presence of the wetland. Multiple Comparison of several Hydrological outputs are observed from several Variability in non-wetland basins with varying catchments, each containing different proportions characteristics amongst several proportions of wetland of wetland. Differences between the outputs are catchments attributed to greater or lesser presence of wetland. In-out Comparison of inflows and Hydrological inputs and outputs associated with outflows of a wetland system a single wetland are measured. Differences between inputs and outputs are attributed to the presence of the wetland. Same Comparison of wetland Hydrological outputs from a single wetland are hydrological response with measured as well as outputs from other non- response elsewhere in the wetland portions of the same catchment. same basin Differences between the outputs are attributed to the wetland. Comp Conclusions relating to Individual component processes are observed and Extrapolation of a single process in a individual components of the understood within a single wetland. The isolation. Processes may not be wetland through the develop- understanding of the processes is the basis for homogeneous across the entire ment of an understanding of a inferring the influence of that process on the wetland. component process hydrological output. (Substituting for : T = topography, a V = vegetation, S = Soil, WC = water content, GW = groundwater, ET = evaporation)

361 Andy Bullock and Mike Acreman publications as the basis for inferring wetland function. Each of past studies. Annex 1 presents the product of the basis has some limitations, and these are summarised. Again, application of the global review. The database is composed abbreviated codes are set out. of 169 different published studies with 440 functional statements, representing the fullest sample of studies that Page number: Page number in the original publication on could be traced, conforming to the principles adopted. It which the conclusion is drawn. would not be claimed that the sample is exhaustive, but it is considered to be comprehensive. Hydrological measure: There are many different measures in hydrology to describe and define aspects of the flow BALANCE OF SCIENTIFIC EVIDENCE FOR regime. While non-hydrologists might refer generically to PARTICULAR HYDROLOGICAL MEASURES floods, the hydrologist would be concerned with measures such as the magnitude of the peak flow during the flood event, the volume of runoff contained in the event, and the Table 5(a to e) collates the number of functional statements time-to-peak. Published studies in wetland hydrology are for each wetland type for the five principal groups of water not consistent in their attention to different measures; it is quantity measures. For example, interpreting Table 5a for possible to find one study analysing the return period of floodplain-type wetlands, two studies conclude that an flood peaks extracted from a 20 or 30 year flow record, and example of this wetland type increases mean annual flow, another analysing the flood volume of a single event, with two studies concludes that no significant influence can be both drawing conclusions on wetland influences on floods. detected and eight studies conclude that examples of this wetland type reduce mean annual flow. Total numbers of Table 4 presents and defines different hydrological measures functional statements are presented across all hydrological within five broad groupings of hydrological response, measures and all wetland types. namely; gross water balance, groundwater recharge, base Analysis of the “balance of scientific evidence” draws on flow and low flows, flood response and river flow variability, comparison of the number of papers that conclude a including some seasonal variations. particular function. This is seen to be an important step and a precursor to more detailed exploration of the evidence for Summary of wetland water quantity function: particular measures for specific wetland types. The results Conclusions regarding water quantity functions extracted cannot yet be considered to reflect a “balance of scientific directly, or in paraphrased form, from the original text are opinion”, because there has been no inter-comparison presented. amongst the different studies. There are some cautionary perspectives and some Summary functional statement for hydrological limitations on the comparison that must be stated. measure: Functional statements of the form ‘wetlands (1) The number of papers reporting a particular influence increase low flows’ are expressed as the sign of the wetland on the water cycle does not necessarily indicate the total influence upon the hydrological measure; thus ‘+’ indicates picture. Some hydrological functions have been studied an increasing influence upon the hydrological measure, ‘-’ more than others. indicates a reducing influence and ‘.’ represents a neutral (2) The number of functional statements cannot be influence (i.e. no significant influence exists or can be interpreted as the number of wetlands performing a detected). In the case of groundwater recharge and function; for example, a functional statement based on groundwater discharge sites, there is interest in the multiple catchments commonly involves a large number conservation-based literature whether either of these of individual wetlands. functions is, or is not, present in a wetland. Therefore, ‘=’ (3) There is no certainty that the 169 publications represent indicates that this function is present and ‘x’ indicates that all past studies of wetlands Although not exhaustive, it is not. the sampling method has been applied independently of any initial bias associated with policy interests. Global data base of wetland water However, it cannot be discounted that there is potential bias in the wetlands that were selected for study by the quantity functions original authors. The first objective of this paper is to redress the deficiency (4) The distribution of wetland types within the sample of in availability of hydrological information on wetland reviewed studies does not represent the distribution of functions by providing an accessible and consistent database wetland types worldwide; this is particularly true given

362 The role of wetlands in the hydrological cycle

Table 4. Hydrological measures and their definition

CODE Hydrological measure Definition

GROSS WATER BALALNCE MAF Mean annual flow Volume (or rate) of river flow during a year (on average) MAAE Mean annual actual evaporation Volume (or rate) of evaporation during a year (on average) WPF Wet period flow Volume (or rate) of river flow during, or in response to, periods of rainfall WPAE Wet period actual evaporation Volume (or rate) of evaporation during, or in response to, periods of rainfall DPAE Dry period actual evaporation Volume (or rate) of evaporation during periods without rainfall Dry period flow See ‘DPFV’ - Dry period flow volume

GROUNDWATER RECHARGE AGR Annual groundwater recharge Volume of water moving vertically from the wetland into the underlying groundwater system during a year WPGR Wet period groundwater recharge Volume of water moving vertically from the wetland into the underlying groundwater system during, or in response to, periods of rainfall DPGR Dry period groundwater recharge Volume of water moving vertically from the wetland into the underlying groundwater system during periods without rainfall

BASE FLOW AND LOW FLOWS GDS Groundwater discharge site Movement of groundwater into surface water through the wetland DPFV Dry period flow volume Volume of flow during dry periods DPFD Dry period flow duration Duration for which flow is sustained during dry periods DPRR Dry period recession rate Rate of flow recession during periods without rain; a high rate indicates a rapid decrease in flow, a low rate indicates sustained low flows

FLOOD RESPONSE FPLM Flood peak of low return period Peak flow during a flood event, where the flow is exceeded on average (T <2 years) every two years or less FPHM Flood peak of high return period Peak flow during a flood event, where the flow is exceeded on average (T > 2 years) every two years or more FEV Flood event volume Total volume of flow during an individual flood event FTTP Flood time-to-peak Time between the onset and peak of a flood event FRR Flood recession rate The recession rate of a flood event

RIVER FLOW VARIABILITY FVa Flow variability Flow variability within the full flow regime WPFVa Wet period flow variability Flow variability during, or in response to, periods with rainfall DPFVa Dry period flow variability Flow variability during periods without rainfall

the focus of studies on North America. Consequently, to the science of wetland hydrology. one cannot necessarily transfer the results of this study (6) No attempt has been made at cross-correlation of to the general grouping of ‘worldwide wetlands’. hydrological measures within single studies. For (5) Conclusions are presented as stated in the original paper; example, if a study has concluded that a particular no attempt is made to evaluate or uphold the conclusions wetland increases evaporation, no conclusion is drawn that are drawn. Further work in the critical evaluation that flow is reduced, unless that explicit statement is of past studies would represent a valuable contribution made by the author.

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Table 5

a Gross water balance FP SW/D SW/S GW/D GW/S General Total Mean annual flow MAF + 2 2 4 - 81517123 . 214 8116 Mean annual actual evaporation MAAE+ 121416125 -123 . 111 3 Wet period flow WPF + 1 3 5 6 15 -1 225 .1111 4 Wet period actual evaporation WPAE + 1 1 -112 . 0 Dry period actual evaporation DPAE + 4 3 15 22 -11 . 0 increased flow or reduced evaporation304111625 reduced flow or increased evaporation 25 2 12 2 30 5 76 not increased or reduced43519123

b. Groundwater recharge FP SW/D SW/S GW/D GW/S General Total Annual groundwater recharge AGR + 1 1 2 1 5 -1 2 47 . 211 4 X 1 517216 = 84246226 Wet period groundwater recharge WPGR + 1 1 - 0 . 0 X1 1 =1111 4 Dry period groundwater recharge DPGR + 0 -11 2 . 0 X1 1 =11 2 increased recharge1101216 decreased recharge1130049 not increased or decreased0021104 recharge does not occur12517218 recharge occurs96357232

c. Base flow and low flow FP SW/D SW/S GW/D GW/S General Total Groundwater discharge site GDS = 2 4 3 18 27 X2215 Dry period flow volume DPFV + 3 1 1 6 3 14 -5 11122847 . 1 412210 Dry period flow duration DPFD + 0 -112 68 . 0 Dry period recession rate DPRR + 1 1 2 - 0 . 0 low flows sustained31107416 low flows diminished 5 0 12 1 23 8 49 not sustained or diminished10412210 groundwater discharge does not occur0220105 groundwater discharge occurs240318027 364 The role of wetlands in the hydrological cycle

d. Flood response FP SW/D SW/S GW/D GW/S General Total Floodpeak low magnitude (T>5 yrs) FPLM+172111 - 1217110738 .23229 Floodpeak high magnitude (T<5 yrFPHM + 1 1 - 41 1118 .1247 Flood event volume FEV + 1 3 6 1 11 -41319 . 0 Flood time to peak FTTP + 3 2 1 6 -1 1 .1 1 Flood recession rate FRR + 1 1 -538 . 0 floods increased or advanced or recession reduced 3 0 15 0 12 2 32 floods reduced or delayed or recession increased 23 2 11 2 15 9 62 not increase, reduced, delayed or advanced20504617

e. River flow variability FP SW/D SW/S GW/D GW/S General Total Flow variability FVa + 5 4 1 10 - 612 0110 .1326 Wet period flow variability WPFVa + 1 1 2 - 0 . 0 Dry period flow variability DPFVa + 0 - 0 . 0 flow variability increased 00605112 flow variability decreased61200110 not increased or decreased1030206

The association between hydrological types and local terms from North America (including 23 different U.S. States and is presented in Table 6. It is immediately evident that there six Canadian Provinces/Territories), with additionally 33 is no strong linkage between hydrological categorisation as studies from 14 countries in Europe, 27 studies from 10 applied in this paper and the use of local or ecological countries in Africa and 17 from elsewhere (including New wetland terms; the terms peat, bog, marsh (and several Zealand (2), Australia, Brazil (3), India, Indonesia and others) recur in different hydrological types. Thus, grouping Malaysia). This distribution reflects the substantial by hydrological type is seen as more meaningful than investment in scientific enquiry in North America compared grouping by local terms. For example, the term ‘bog’ can with other regions of the world and a relative dearth of be found in all five hydrological types. accessible information relating to Asian and South American From a hydrological perspective, the content of the wetland hydrology. database may be perceived as limited due to its emphasis The term ‘wetland’ embraces a wide variety of land types, on functions rather than hydrological processes — given from springs to large inland deltas. As a result, a lack of that the concept of functions is not well-established within consistency in the impact of wetlands on the water cycle the hydrological community. However, while more process was anticipated. Unique conclusions concerning any specific information can be extracted from the set of publications, hydrological function cannot be drawn for all wetlands. the target of this paper is the use of functional generalisations Taking flow variability as a single hydrological measure, to represent wetland hydrology to the wetland management for example, there are 28 statements with good geographical and policy arena. Clearly, there is a strong case for bringing coverage, of which 10 show that variability is increased by hydrological processes and function closer together. wetlands, 11 that variability is reduced, and 6 that wetland Geographically, the dataset is dominated by 92 studies influence is neutral. When wetlands are sub-divided into

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Table 6. Wetland hydrological types and local terms

Type Code Local terms

Floodplain FP Sudd, river valley, swamp, floodplain, valley bog, marsh, cypress swamp, delta (inland), dambo, marsh, inland valley swamps and bolis, pantanal Surface water depression SW/D Bog, prairie pothole, slough, kettle-hole, shallow depressions Surface water slope SW/S Perched bog, peat, peat bog, pond, raised bog, blanket peat, muck, pocosin, saturated heath, palsa, aapa-mire, infilled lakes, constructed wetland Groundwater depression GW/D Marsh, prairie pothole, fen, pond, bog Groundwater slope GW/S Swamp, marsh, river valley, bog, dambo, fen bogs, peat bog, peat, wetland, pocosin, macrophytes, cypress domes, peat fen, pakahi, fen, mire, blanket bog, quaking fen, pond, domed bog and fen General Swamp, bog, marsh, ‘basin storage’, ponds, hydromorphic gleys, forest wetland

hydrologically similar types, greater consistency of The main conclusions of the analysis are as follows. conclusion emerges — six of seven conclusions from studies of floodplains conclude that flow variability is reduced by 1. Wetlands are significant in altering the water cycle. The wetlands (including the Sudd and Okavango in Africa and 169 scientific studies published during the period 1930– Barito in Indonesia). But ambiguity still exists: amongst 19 2002 (as traced by this paper) provide 439 statements studies of headwater wetlands (all from USA and Europe), on the hydrological significance of wetlands. Of the 10 studies conclude that flow variability is increased; 5 that 439 statements, only 83 (19%) conclude the wetland the wetland influence is neutral; and 4 that variability is influence on the water cycle to be neutral or reduced. Even apparently similar wetlands perform insignificant. The vast majority conclude that wetlands functions that are seemingly in opposition (e.g. peat bogs either increase or decrease a particular component of occur in each of the three categories; increasing, decreasing the water cycle. It is this evidence that has led to the and not-affecting flow variability). But unanimity of notion that wetlands perform hydrological functions. function is not anticipated — there is no prior assumption Since wetlands cover approximately 6% of the world’s that all wetlands of a particular type perform the same land area, with many linked directly to rivers and function. This study has not yet investigated the detailed aquifers, this is an issue of importance to water climatology, catchment conditions and internal wetland management. structure, any of which can mean a particular wetland will 2. There are some significant generalisations that emerge perform differently from other wetlands that are otherwise from the published hydrological evidence. These are similar. different from the long-standing generalisation that Whether hydrological functions of wetlands are wetlands always reduce floods, promote groundwater considered to be beneficial or not depends upon one’s point recharge and regulate river flows. Most, but not all, of view. For example, ecologists may see evaporation from studies (23 of 28) show that floodplain wetlands reduce wetlands as an essential process supporting plant growth, or delay floods, with examples from all regions of the whilst water resource managers may see it as a loss of a world. This same influence on floods is also seen, but vital downstream resource. Those living in flood-prone areas less conclusively (30 of 66) for wetlands in the downstream of wetlands that generate floods may view them headwaters of river systems (e.g. bogs and river negatively while those living downstream of wetlands that margins). A substantial number (27 of 66) of headwater reduce floods may not view them in the same light. wetlands increases flood peaks. These studies were Ecologists see floods as essential elements of the river flow mostly from Europe, but included work from West regime maintaining channel structure through sediment Africa and Southern Africa. Around half of the transport, and interactions between the river and its statements (11 of 20) for flood event volumes and 8 of floodplain that drives nutrient exchange and breeding cycles 13 for wet period flows) show that headwater wetlands (Junk et al., 1989, Poff et al., 1997). increase the immediate response of rivers to rainfall,

366 The role of wetlands in the hydrological cycle

generating higher volumes of flood flow, even if the Implications of the results for wetland flood peak is not increased. The coverage of these research and policy formulation studies is world-wide including Africa and South America. This function occurs because headwater This paper confirms that wetlands exert a strong influence wetlands tend to be saturated and convey rainfall rapidly on the hydrological cycle. It strengthens the view that to the river; thus they are a principal mechanism for management of wetlands must be an important part of generation of flood flows. integrated water resources and flood management of all river 3. There is strong evidence that wetlands evaporate more basins. Where wetlands reduce floods, recharge groundwater water that other land types, such as forests, savannah and increase dry season flows, wetland hydrology is working grassland or arable land. Two thirds of studies (48 of in sympathy with water resources managers and flood 74) conclude that wetlands increase average annual defence engineers. Where wetlands have high evaporation evaporation or reduce average annual river flow. About demands or generate flood-runoff, they may create or 10% of studies (7) conclude the opposite; for example exacerbate water management problems. Whatever the some woodlands in Zambia had greater evaporation than hydrological functions they perform, decisions on wetland the adjacent wetlands. The remaining 25% are neutral. conservation will inevitably be taken in a wider context and There is no obvious distinction amongst different will also depend on water scarcity and on other functions, wetland sub-types or geographical regions of the world. such as human health, fisheries, navigation, recreation, 4. Two-thirds of studies (47 of 71) conclude that wetlands cultural heritage and biodiversity. reduce the flow of water in downstream rivers during Successful water management requires knowledge of the dry periods. Evidence is mainly from North America extent to which wetlands are performing different and Europe, but includes floodplains in Sierra Leone hydrological functions. Since it is not feasible to study every and wetlands in Southern Africa. This is backed by wetland in detail, rapid assessment methods are required to overwhelming evidence (22 of 23 studies) that shows identify likely functions. Furthermore, a major objective of evaporation from wetlands to be higher than from non- this work is to stimulate discussion on hydrological wetland portions of the catchment during dry periods. functions. It is relatively easy to add to the database, either There is no discernible difference for different wetland within additional previously published work or through new sub-types. In 20% of cases, wetlands increase river research. It is harder to account for variations in functions. flows during the dry season. For it is clear that there is no simple relationship between 5. Many wetlands exist because they overlie impermeable wetland types and the hydrological functions they perform. soils or rocks and there is little interaction with Part of the problem steps from the lack of a simple groundwater. The database contains 69 statements classification of wetlands that consistently relates hydrology, referring to groundwater recharge; 32 conclude merely vegetation, substrate type and geomorphology. It is unlikely that recharge takes place, and 18 conclude there is no that any sophisticated classification scheme would be able recharge. There are similar numbers of studies that to explain the variation of function in evidence. report wetlands either to recharge more (6) or less than Various methods have been developed in a number of (9) other land types. Some wetlands, such as floodplains countries around the world to assess hydrological functions in India and West Africa on sandy soils, recharge of wetlands. Some are merely classification systems that groundwater when flooded. Many wetlands have group wetlands according to botanical, geomorphological formed at springs and are fed by groundwater. The and/or water regime characteristics (e.g. Cowardine et al., direction of water movement between the wetland and 1979; Brinson, 1993; Gilvear and McInnes, 1994; Wheeler, the ground may change in the same wetland, such as in 1984). Other methods give each wetland a grade for a some peatlands in Madagascar, according to function, such as high medium or low (e.g. Adamus et al., hydrological conditions. 1987) or produce a quantitative estimate of performance of 6. Conclusions have been drawn above on flow variability. a given function (e.g. Amman and Stone, 1991; Hruby et The over-riding picture appears to be a reduction in al., 1995). Maltby et al. (1996) have developed a framework flood peaks by floodplains. In some cases, such as many of functional analysis through characterisation of distinct headwater wetlands, increasing flood flows combines ecosystem/landscape units (termed hydrogeomorphic units). with decreasing dry season flows to widen the overall The objective is to provide a simple and rapid procedure, range of flows. but the system still needs to be operationalised. In addition, guides have been produced for extending the functional assessment to produce an economic value for the functions

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(Lipton et al., 1995, Barbier et al., 1995). Recent work in Balek, J., 1977. Chapter 7: Swamps. In: Hydrology and water the UK (Wheeler and Shaw, 2000) used data from over 80 resources in tropical Africa, A. Millington (Ed) Elsevier, Amstrerdam, The Netherlands. 154–168. wetlands in Eastern England to develop a classification and Barbier, E.B., Acreman, M.C. and Knowler, D., 1997. Economic assessment system called WETMECS that combines valuation of wetlands: a guide for policy makers and planners. landscape situation, water supply mechanism, Ramsar Convention, Gland, Switzerland. Bardecki, M., 1984. What value wetlands? J. Soil Water Conserv., hydrotopographical elements, acidity (base-richness) and 166–169. fertility. The outcome of this study is that apparently similar Bardecki, M., 1987. Cumulative impacts of agricultural land wetlands are driven by very different hydrological processes; drainage on watershed hydrology. Proc. Nat. Wetland Symp. on ‘Wetland Hydrology’, Association of Wetland Managers Inc, almost invariably, some data need to be collected at a site to Chicago, USA. 124–129. identify its functional role. Bavina, L.G. 1975. Water balance of swamps in the forest zone of Consequently, generalised and simplified statements of the European part of the USSR. In: Hydrology of marsh-ridden wetland function are discouraged because they demonstrably areas, Proc. of the Minsk Symp. (June, 1972), International Association of Hydrological Sciences. UNESCO/IAHS, Paris. have little practical value. As a minimum, this paper 297–304. encourages the future representation of diversity and Bay, R.R., 1967. Groundwater and vegetation in two peat bogs in complexity amongst wetlands and the portrayal of diverse Northern Minnesota. Ecology, 48, 308–310. Bay, R.R., 1969. Runoff from small peat watersheds. J. Hydrol., hydrological functions. 9, 90–102. Hydrologists must be more imaginative and proactive in Bedinger, M.S., 1981. Hydrology of bottomland hardwood forests contributing scientific knowledge to underpin policy of the Mississippi Embayment. In: Wetlands of bottomland hardwood forests, J.R.Clark and J. Benforado (Eds.), Elsevier, formulation and management decisions. For the hydrological The Netherlands. 161–176. community, a new challenge is set for wetland policy. Boelter, D.H. and Verry, E. S., 1977. Peatland and water in the Northern Lake States. General Tech. Rep. NC-31, US Dept Agricultural Forestry Service, North Central Experimental Acknowledgements Station, St. Paul Minnesota, USA. 22pp. Boeye, D. and Verheyen, R.F., 1992. The hydrological balance of Financial support to Mike Acreman for this work was a groundwater discharge fen. J. Hydrol., 137, 149–163. provided by IUCN — The World Conservation Union. Brandesten, C.O., 1988. Seasonal variation in streamflow recessions in the mire complex Komosse, Southern Central Comments on the draft of an earlier paper by unknown Sweden. Symposium on the Hydrology of wetlands in temperate referees are acknowledged. Comments on the draft of this and cold regions: Vol 1. Academy of Finland, Helsinki. 84–91. paper were provided by Dr Jean-Yves Pirot and other staff Brinson, M.M., 1993. A hydro-geomorphic classification for from IUCN. Dr David Gasca of Atkins made additional wetlands. Technical Report WRP-DF-4. US Army Engineers Waterways Experimental Station, Vicksburg, Mississippi, USA. contributions to the database. Brooks, K.N. and Kreft, D.R., 1989. A hydrologic model for Minnesota Peatlands. J. Minnesota Acad. Sci., 55, 113–119. Brown, S.L., 1990. Structure and dynamics of basin forested References wetlands in North America. In: Forested wetland ecosystems of the world. A.E. Lugo, M.M. Brinso and S.L. Brown (Eds.) Ackroyd, E.A., Walton W.C. and Hills D.L., 1967. Groundwater Elsevier, Amsterdam, The Netherlands. 171–199. contribution to streamflow and its relation to basin Brun, L.J., Richardson, J.L., Enz, J.W. and Larsen, J.K., 1981. characteristics in Minnesota. Report of Investigations No.6, Streamflow changes in the Southern Red River Valley of North University of Minnesota, USA. Dakota. North Dakota Farm Research, 38, 11–14. Adamus, P.R. and Stockwell, L.T., 1983. A method for wetland Bucher, E.H., Bonetto, A., Boyle T., Canevari P., Castro G., Huszar functional assessment: Volume I, Critical review and evaluation P. and Stone, T., 1993. Hidrovia- an initial environmental concepts. Federal Highway Agency FHWA-IP-82-23, U.S. Dept. examination of the Paraguay - Parana waterway. Wetlands for of Transporation, Washington, USA. 176pp. the Americas Publication No. 10, Manomet, MA, USA, 72pp. Adamus, P.R. et al., 1987. Wetland evaluation technique (WET) Bulavko A.G. and Drozd V.V., 1975. Bog reclamation and its effect volume II: Methodology. US Army Corp. Engineers, Vicksburg, on the water balance of river basins. Hydrology of marsh-ridden Mississippi State. areas, Proc. of the Minsk Symp. (June, 1972), International Amman, A. and Stone, A.L., 1991. Method for comparative Association of Hydrological Sciences, UNESCO/IAHS, Paris. evaluation of non-tidal wetlands in New Hampshire. New 461–468. Hampshire Department of Environmental Services. NHDES- Bullock, A., 1992a. The role of dambos in determing river flow WRD-1991-3 regimes in Zimbabwe. J. Hydrol., 134, 349–372. Baden, W. and Eggelsmann, R., 1986. The hydrologic budget of Bullock, A., 1992b. Dambo hydrology in Southern Africa: review the Highbogs in the Atlantic region. Proc. Third International and reassessment. J. Hydrol., 134, 373–396. Peat Congress, Dept. Energ. Mines & Resourc.; Nat. Research Burke, W., 1968. Drainage of blanket peat at Glenamoy. Proc. Council, Ottawa, Ontario, Canada, 206–211. 2nd International Peat Congress. HMSO, Edinburgh, UK. 809– Balek, J. and Perry J.E., 1973. Hydrology of seasonally inundated 817. African headwater swamps. J. Hydrol., 19, 227–249.

368 The role of wetlands in the hydrological cycle

Burke, W., 1975. Aspects of the hydrology of blanket peat in Eisenlohr, W.S., 1975. Hydrology of marshy ponds on the coteau Ireland. Hydrology of marsh-ridden areas, Proc. of the Minsk du Missouri. Hydrology of marsh-ridden areas, Proc. of the Symp. (June, 1972), International Association of Hydrological Minsk Symp. (June, 1972), International Association of Sciences, UNESCO/IAHS, Paris. 171–182. Hydrological Sciences, UNESCO/IAHS, Paris. 305–312. Burt, T.P., 1995. The role of wetlands in runoff generation from Egglesmann, R., 1975. The water balance of lowland areas in headwater catchments. In: Hydrology and hydrochemistry of north-western regions of the FRG. Hydrology of marsh-ridden British wetlands, J. Hughes and L. Heathwaite (Eds.) Wiley, areas, Proc. of the Minsk Symp. (June, 1972), International Chichester, UK. 21–38 Association of Hydrological Sciences, UNESCO/IAHS, Paris. Campbell, R.E. and Drecher, F.C., 1970. A proposed streamflow 355–368. data program for Wisconsin: Madison, Wisconsin, U.S. Geol. Eggelsmann, R., Heathwaite, A.L., Grosse-Brauckmann, G., Surv. Open File Rep., 55pp. Kuster, E., Naucke, W., Schuch, M. and Schweickle, 1993. Carter, V., 1986. An overview of the hydrologic concerns related Physical processes and properties of mires. In: Mires: process, to wetlands in the United States. Can. J. Bot., 64, 364–374. exploitation and conservation, A.L. Heathwaite and Kh. Gottlich CEC, 1995. Wise use and conservation of wetlands. (Eds.). Wiley, Chichester, UK. 171–262. Communication from the Commission to the Council and the Faulkner, R.D. and Lambert, R.A., 1991. The effect of dambo European Parliament, Commission of the European irrigation on dambo hydrology: a case study. J. Hydrol., 123, Communities COM(95) 189 (final), 54pp. 147–161. Choi, J. and Harvey, J.W., 2000. Quantifying time-varying Ferrari, M.R., Miller, J.R. and Russell, G.L., 1999. Modeling the groundwater discharge and recharge in wetlands of the Northern effect of wetlands, flooding and irrigation on river flow; Florida Everglades. Wetlands. 20, 500–511. application to the Aral Sea. Water Resour. Res., 35, 1869–1876. Conger, S., 1971. Estimating magnitude and frequency of floods Flippo, H.N. Jnr., 1977. Floods in Pennsylvania: Pennsylvania in Wisconsin: Madison, Wisconsin, U.S. Geological Survey Department of Environmental Resources, Water Resour. Bull., open-file report, 200pp. 13, 59. Cowardine, L.M. et al., 1979. Classification of wetlands and Ford, J. and Bedford, B.L., 1987. The hydrology of Alaskan deepwater habitats of the United States. US Fish and Wildlife wetlands, U.S.A.; a review. Arctic Alp. Res., 19, 209–229. Service FWS/OBS-79/31. 103 pp. Forest, W.E. and Walker, P.N., 1970. A proposed streamflow data Daniel, C., 1981. Hydrology, geology and soils of pocosins: a program for Maryland and Delaware, Towson, Maryland, U.S. comparison of natural and altered systems. In: Pocosin Wetlands, Geol. Surv. Open File Rep. 41pp. C. J. Richardson (Ed.). Hutchinson Ross Publ. Co., Straudsburg, Freeze, R.A., 1969. Hydrology of the Good Spirit Lake Drainage 109–124. Basin, Saskatchewan - a preliminary analysis. Inland Waters Darmer, K.I., 1970. A proposed streamflow data program for Branch Tech. Bull. No.14, Dept. of Energy, Mines and New York: Albany, New York, U.S. Geological Survey open- Resources, Canada. file report. 29pp. Gehrels J. and Mulamoottil, G., 1990. Hydrologic process in a Davies, J., Claridge C.F., 1993. Wetland benefits: the potential southern Ontario wetland. Hydrobiologia, 208, 221–234. for wetlands to support and maintain development. Asian Genereux, D. and Slater, E., 1999. Water exchange between canals Wetland Bureau Publication No. 87: IWRB Spec. Publ. 27: and surrounding aquifer and wetlands in Southern Everglades, Wetlands for the America Publication No. 11. Asian Wetland USA. J. Hydrol., 219, 153–168. Bureau, Kuala Lumpur, Malaysia, 45pp. Gerla, P.J., 1999. Estimating the groundwater contribution in Davis, T.J., 1993. Towards the wise use of wetlands. Ramsar wetlands using modelling and digital terrain analysis. Wetlands, Convention Bureau, Gland Switzerland, 180pp. 19, 394–402. Demissie, M., Khan A. and al-Mubarak, R., 1991. Influence of Gerla, P.J. and Matheney, R.K., 1996. Seasonal variability and wetlands on streamflow in Illinois. Proc. ASCE Nat. Conf. on simulation of groundwater flow in a prairie wetland. Hydrol. Hydraulic Engineering, 949–954. Process., 10, 903–920. Demissie, M. and Khan A., 1991. Wetland drainage and streamflow Gibson, J.J., Edwards, T.W.D. and Prowse, T.D., 1993. Runoff trends in Illinois. Proc. ASCE Nat. Conf. on Hydraulic generation in a high boreal wetland in northern Canada. Nord. Engineering, 1050–1054. Hydrol., 24, 213–224. Doss, P.K., 1995. Physical-hydrogeologic processes in wetlands. Gilvear, D.J., Andrews, R., Tellam, J.H., Lloyd, J.W. and Lerner, Nat. Area. J., 15, 216–226. D.N., 1993. Quantification of the water balance and Doyle, A.F., 1987. The Charles River Watershed: a dual approach hydrogeological processes in the vicinity of a small to floodplain management. Proc. Nat. Wetland Symp on Wetland groundwater-fed wetland, East Anglia, U.K.. J. Hydrol., 144, Hydrology. Assoc. of State Wetland Managers Inc., Chicago 311–334. 110–112. Gilvear, D. and McInnes, R.J., 1994. Wetland hydrological Drayton, R.S., Kidd, C.H.R., Mandeville, A.N. and Miller, J.B., vulnerability and the use of classification procedures: a Scottish 1980. A regional analysis of river floods and low flows in case study. J. Environ. Manage., 42, 403–414. Malawi. Institute of Hydrology Report No. 72, Wallingford, UK Gilliam, J.W. and Skaggs, R.W., 1981. Drainage and agricultural Dubreuil, P.L., 1985. Review of field observations of runoff development: effects on drainage waters. In: Pocosin Wetlands, generation in the tropics. J. Hydrol., 80, 237–264. C. J. Richardson (Ed.), Hutchinson Ross Publ. Co., Straudsburg, Dugan, P. J., 1990. Wetland conservation - a review of current 109–124. issues and required action. IUCN - The World Conservation Glazacheva, L.I., 1975. The effect of reclamation on rivers and Union, Gland, Switzerland, 96pp. lakes in Latvia. In Hydrology of marsh-ridden areas, Proc. of Eisenlohr, W.S., 1972. Hydrologic investigations of prairie the Minsk Symp. (June, 1972), International Association of potholes in North Dakota, 1959–1968. Geological Survey Hydrological Sciences, UNESCO/IAHS, Paris. 513–518. Professional Paper 585-A, US Govt. Printing Office, Gonthier, G.J., 1996. Groundwater flow conditions within a Washington, 102 pp. bottomland hardwood wetland, Eastern Arkensas. Wetlands, 16, 334–346.

369 Andy Bullock and Mike Acreman

Grillot, J.C. and Dussarrat, B., 1992. Hydraulique des unites Hommik, K.T. and Madissoon, G.I., 1975. The influence of fen d’interfluves et de bas-fond tourbeux: un example en zone de bog drainage on annual runoff in the Estonian SSR. Hydrology socle altere (Madagascar). J. Hydrol., 135, 321–340. of marsh-ridden areas, Proc. of the Minsk Symp. (June, 1972), Gurnell, A.M. and Gregory, K.J., 1986. Water table level and International Association of Hydrological Sciences, UNESCO/ contributing area: the generation of runoff in a heathland IAHS, Paris. 487–492. catchment. In: Conjunctive Water Use, S.M. Gorelick (Ed.), Hooijer, A., 1996. Floodplain hydrology: an ecologically oriented IAHS Publ. no. 156, 87–95. study of the Shannon Callows, Ireland. Amsterdam University, Hall, F.R., Rutherford, R.J. and Byers, G.E., 1972. The influence The Netherlands. of a New England wetland on water quantity and quality. Res. Howard-Williams, C., 1983. Wetland and watershed management: Rep. 4, Wat. Resour. Res. Centre, New Hampshire University, the role of aquatic vegetation. J. Limnol. Soc. S. Afr., 9, 54–62. Durham, NH, USA. Howe, C.P., Claridge, G.F., Hughes, R. and Zuwendra, 1992. Hamilton, S.K., Sippel, S.J., Calheiros, D.F. and Melack, J.M., Manual of guidelines for scoping EIA in tropical wetlands. 2nd 1997. An anoxic event and other biogeochemical effects of the Edition, Asian Wetland Bureau-Indonesia, Bogor, Indonesia, Pantanal wetland on the Paraguay River. Limnol. Oceanogr., 261pp. 42, 257–272. Hruby, T. et al., 1995. Estimating relative wetland values for Hardy, R.J., Bates, P.D. and Anderson, M.G., 2000. Modelling regional planning. Wetlands, 15, 93–107. suspended sediment deposition on a fluvial floodplain using a Hunt, R.J., Krabbenhoft, D.P. and Anderson, M.P., 1996. two-dimensional dynamic finite element model. J. Hydrol., 229, Groundwater inflow measurement in wetland systems. Water 202–218. Resour. Res., 32, 495–507. Hayashi, M., van der Kamp, G. and Rudolph, D.L., 1998a. Water Hurst, H.E., 1933. The Sudd region of the Nile. J. Roy. Soc. Arts,. and solute transfer between a prairie wetland and adjacent 81, 721–736. uplands. 1. Water balance. J. Hydrol., 207, 42–55. Iritz, L., Johansoon, B. and Lundin, L., 1994. Impacts of forest Hayashi, M., van der Kamp, G. and Rudolph, D.L., 1998b.Water dranage on floods. Hydrolog. Sci. J., 39, 637–661. and solute transfer between a prairie wetland and adjacent Ingram, H.A.P., 1983. Hydrology. In: Ecosystems of the World. uplands. 2. Chloride balance. J. Hydrol., 207, 56–67. 4A: Mires: swamp, bog, fen and moor, A.J.P. Gore (Ed.), Heikurainen, L., 1976. Comparison between runoff conditions on Elsevier, Amsterdam, The Netherlands. 67–158. a virgin peatland and a forest drainage area. Proc. Fifth Jackson, R.J., 1987. Hydrology of an acid wetland before and International Peat Congress. 76–86. after draining for afforestation, western New Zealand. In: Forest Heimburg, K., 1984. Hydrology of North-Central Florida cypress Hydrology and Watershed Management, R.H Swanson (Ed), domes. In: Cypress Swamps, K.C. Ewel. and H.T. Odum (Eds.), Proc. of the Vancouver Symposium, IAHS Publ. no. 167, 465– Univ. of Florida, Gainsville, USA. 72–82. 474. Hemond, H.F., 1980. Biogeochemistry of Thoreau’s Bog, Concord, Johansson, B. and Seuna, P., 1994. Modelling the effects of wetland Massachusetts. Ecol. Monogr., 50, 507–526. drainage on high flows. Aqua Fennica 24, 59–68. Hensel, B.R. and Miller, M.V., 1991. Effects of wetland creation John, D.M., Leveque, C. and Newton, L.E., 1993. Chapter on on groundwater flow. J. Hydrol., 126, 293–314. West Africa. In: Wetlands of the World I: Inventory, ecology Hewlett, J.D. and Hibbert, A.R., 1967. Factors affecting the and management, D.F. Whigham, D. Dykyjova and S. Hejny response of small watersheds to precipitation in humid regions. (Eds.), Kluwer, Dordrecht, The Netherlands. In: Forest Hydrology, W.E. Sopper and H.W. Lull (Eds.) Junk, W.J., Bayley, P.B. and Sparks, R.E., 1989. The flood pulse Pergamon Press, Oxford., UK, 275–290. concept in river-floodplain systems. Can. J. Fisheries Aquat. Hey, D.L., Barrett, K.R. and Biegen, C., 1994. The hydrology of Sci., 106, 110–127. four experimental constructed wetlands. Ecol. Eng., 3, 319– Keough, J.R. and Pippen, R.W., 1984. The movement of water 343. from peatland into surrounding groundwater. Can. J. Bot., 62, Hickok, E.A., Hannaman, M.C. and Wenck, N.C., 1977. Urban 835–839. runoff treatment methods. Volume 1. Non-structural wetlands Khan, N., 1995. Protection of North Selangor Peat Swamp Forest, treatment. U.S. EPA-600/2-77-217. NTIS Report No. PB-278- Malaysia. Parks, 5, 24–31. 172/2ST. Kiselev, P.A., 1975. Study of the water balance of stratified aquifers Hill, J.L. and Kidd, C.H.R., 1980. Rainfall-runoff relationships based on the analysis of their regime during hydrogeological for 47 Malawi catchments. Water Resources Branch, Malawi, investigations on marshy lands and adjacent areas. In: Hydrology No. TR7. 22pp. of marsh-ridden areas, Proc. of the Minsk Symp. (June, 1972), Hillman, G.R., 1998. Floodwave attenuation by a wetland International Association of Hydrological Sciences, UNESCO/ following a beaver dam failure on a second order boreal stream. IAHS, Paris. 35–46. Wetlands, 18, 21–34. Klepper, O., 1992. Model study of the Negara River Basin to assess Hodnett, M.G., Vendrame, I., de O. Marques, F, Oyama, M.D. the regulating role of its wetlands. Regul. River, 7, 311–325. and Tomasella, J., 1997. Soil water storage and groundwater Kloet, L., 1971. Effects of drainage and runoff and flooding within behaviour in a catenary sequence beneath forest in central the Pembina River Basins: North Dakota - Manitoba. Bureau Amazonia. Hydrol. Earth Syst. Sci., 1, 265–277. of Sport, Fisheries and Wildlife, Bismarck, North Dakota Hollis, G.E., 1990. Environmental impacts of development on Klueva, K.A., 1975. The effect of land reclamation by drainage wetlands in arid and semi-arid lands. Hydrolog. Sci. J., 35, 411– on the regime of rivers in Byelorussia. In: Hydrology of marsh- 428. ridden areas, Proc. of the Minsk Symp. (June, 1972), Hollis, G.E., 1996. Hydrological inputs to management policy for International Association of Hydrological Sciences, UNESCO/ the Senegal river and its floodplain. In: Water management and IAHS, Paris. 419–438. wetlands in Sub-Saharan Africa, M.C. Acreman and.G.E. Hollis Koerselman, W., 1989. Groundwater and surface water hydrology (Eds.), IUCN. 155–184. of a small groundwater-fed fen. Wetland Ecol. Manage., 1, 33– 43.

370 The role of wetlands in the hydrological cycle

Konyha, K.D., Robbins, K.D. and Skaggs, R.W., 1988. Evaluating Millington, A.C., 1985. Inland Valley Swamps and bolis in Sierra peat-mining drainage using DRAINMOD. J. Irrig. Drain. Eng., Leone: hydrological and pedological considerations for 114, 490–504. agricultural development. Z. Geomorph. N.F. Suppl. 36, 201– Kovrigo, P.A. and Yatshukno, V.M., 1988. Optimization of the 222. microclimate of bog geosystems. Symposium on the Hydrology Mitsch, W.J., Dorge, C.L. and Wiemhof, J.R., 1977. Forested of wetlands in temperate and cold regions: Vol 2. Academy of wetlands for water resources management in southern Illinois. Finland, Helsinki, 22–29. Report 132, Water Resources Centre, Univ. of Illinois, Urbana. Kowalik, P.J., Banach, K. and Toczylowska, I., 1988. Seepage Mokylak, V.I., Kubyshkin, G.P. and Karkutsiev, G.N., 1975. The component in water balance of peat soils. Symposium on the effect of drainage works on streamflow. Hydrology of marsh- Hydrology of wetlands in temperate and cold regions: Vol 1. ridden areas, Proc. of the Minsk Symp. (June, 1972), Academy of Finland, Helsinki, 178–183. International Association of Hydrological Sciences, UNESCO/ Kusler, J.A. and Riexinger, P., 1986. National wetland assessment IAHS, Paris. 439–446. symposium. Association of State Wetland Managers, New York, Moskvin, Y.P., 1988. Water and energy regime of palsa bogs in USA. West Siberia. Symposium on the Hydrology of wetlands in Lipton, D.W. et al., 1995. Economic valuation of natural resources temperate and cold regions: Vol 2. Academy of Finland, – a handbook for coastal resource policy-makers. US Helsinki, 18–21. environmental Protection Agency. EPA/600/R-92/167. Mustonen, S.E. and Seuna, P., 1975. Influence of forest drainage Littlejohn, C., 1977. An analysis of the role of natural wetlands in on the hydrology of an open bog in Finland. Hydrology of marsh- regional water management. In: Ecosystem modelling in theory ridden areas, Proc. of the Minsk Symp. (June, 1972), and practice C.A.S. Hall and J.W. Day (Eds.), Wiley, International Association of Hydrological Sciences, UNESCO/ Chichester, UK. 451–476. IAHS, Paris 519–530. Logan, W.S. and Rudolph, D.L., 1997. Micro depression-focused NERC, 1975. Flood routing studies: Vol III. Flood Studies Report. recharge in a coastal wetland, La Plata, Argentina. J. Hydrol., Natural Environment Research Council, London, UK. 194, 221–238. Newson, M.D., 1981. Mountain streams, In: British rivers, J. Ludden, A.P., Frank, D.L. and Johnson, D.H., 1983. Water storage Lewin (Ed.), George Allen & Unwin. 59–89. capacity of natural wetland depressions in the Devils Lake Basin Nielsen, S.A., Refsgaard, J.C. and Mathur, V.K., 1991. Conceptual of North Dakota. J. Soil Water Conserv., 38, 45–48. modelling of water loss on floodplains and its application to Lundin, L., 1988. Impacts of drainage for forestry on runoff and River Yamuna upstream of Delhi. Nord. Hydrol., 22, 265–274. water chemistry. Symposium on the Hydrology of wetlands in Nisula, T. and Kuittinen, R., 1988. Snowmelt and runoff in aapa- temperate and cold regions: Vol 1. Academy of Finland, mire in Finnish Lappland. Symposium on the Hydrology of Helsinki, 197–205. wetlands in temperate and cold regions: Vol 1. Academy of Maltby, E., 1991. Wetland management goals: wise use and Finland, Helsinki, 76–83. conservation. Landscape Urban Plan., 20, 9–18. Nortcliff, S. and Thornes, J.B., 1981. Seasonal variations in the Maltby, E., Hogan, D.V. and McInnes, R.J., 1996. Functional hydrology of a small forested catchment near Manaus, analysis of European wetland ecosystems. Report to the Amazonas, and the implications for its management. In: Tropical European Commission. EC DGXII STEP-CT90-0084. Agricultural Hydrology, R. Lal and E.W.Russell, (Eds.) Wiley, Matheney, R.K. and Gerla, P.J., 1996. Environmental isotopic Chichester, UK. 37–58. evidence for the origins of ground and surface water in a prairie Novitski, R.P., 1978. Hydrologic characteristics of Wisconsin’s discharge wetland. Wetlands, 16, 109–120. wetlands and their influence on floods, streamflow and sediment. McCartney, M.P., 2000. The water budget of a headwater In: Wetland functions and values: the state of our understanding, catchment containing a dambo. Phys. Chem. Earth B, 25, 611– Amer. Water. Resour. Assoc., Minneapolis, MN, USA, 377– 616. 388. McComas, M.R., Kempton, J.P. and Hinkley, K.C., 1972. Geology, Novitski, R.P., 1982. Hydrology of Wisconsin wetlands. Univ. of soils and hydrogeology of Volo Bog and vicinity, Lake County, Wisconsin, Geol. and Nat. Hist. Surv. Info. Circular No. 40, Illinois. Environmental Geology Note 57, Ill. State Geol. Surv. 22pp. 27pp. Novitski, R.P., 1985. The effects of lakes and wetlands on flood McKay, E.D., Elzaftawy, A. and Cartwright, K., 1979. flows and base flows in selected northern and eastern States. Groundwater geology of selected wetlands in Union and Proc. Conf. on Wetlands of the Chesapeake, Easton, Maryland, Alexander Counties, Illinois. Environmental Geology Note No. Environmental Law Institute, 143–154. 85, Illinois Inst. of Natural Resources, Urbana, 41pp. Nuckles, D., 1970. Virginia streamflow data program analysis. Meigh, J., 1995. The impact of small farm reservoirs on urban Richmond, Virginia, U.S. Geol. Surv. Open File Rep. 54pp. water supplies in Botswana. Natur. Resour. Forum, 19, 71–83. O’Brien, A.L., 1977. Hydrology of two small wetland basins in Meyboom, P., 1964. Three observations on streamflow depletion Eastern Massachusetts. Water. Resour. Bull.,.13, 325–340. by phreatophytes. J. Hydrol., 2, 248–261. O’Brien, A.L., 1980. The role of groundwater in stream discharges Mikulski, Z. and Lesniak, E., 1975. Hydrological research on a from two small wetland controlled basins in eastern peatbog in the upper Suprasl basin. Hydrology of marsh-ridden Massachusetts. Ground Water, 18, 359–365. areas, Proc. of the Minsk Symp. (June, 1972), International O’Brien, A.L., 1988. Evaluating the cumulative effects of alteration Association of Hydrological Sciences, UNESCO/IAHS, Paris, on New England wetlands. Environ. Manage., 12, 627–636. 55–68. OECD, 1996. Guidelines for aid agencies for improved Miller, E.G., 1965. Effect of Great Swamp, New Jersey, on conservation and sustainable use of tropical and sub-tropical streamflow during base-flow periods. U.S. Geol. Surv. Prof. Pap. wetland. Organisation for Economic Cooperation and 525-B, 177–179. Development Development Assistance Committee: Guidelines on Aid and Environment No.9, 69pp. Ogawa, H. and Male, J.W., 1986. Simulating the flood mitigation role of wetlands. J. Water Resour. Plan. Man. ASCE, 112, 114– 127.

371 Andy Bullock and Mike Acreman

Owen, C.R., 1995. Water budget and flow patterns in an urban Siegel, D.I., 1988. The recharge-discharge influence of tectonic wetland. J. Hydrol. 169, 171–187. setting on the hydrological characteristics of deeply weathered Panu, U.S., 1988. Environmental assessment of peatland terrains: evidence from Uganda. J. Hydrol., 218, 44–71. development operations in Newfoundland. Symposium on the Thompson, J.R. and Hollis, G.E., 1995. Hydrological modelling Hydrology of wetlands in temperate and cold regions: Vol 1. and the sustainable development of the Hadejia-Nguru wetlands, Academy of Finland, Helsinki, 291–300. Nigeria. Hydrolog. Sci. J., 40, 97–108. Phillips, P.J. and Shedlock, R.J., 1993. Hydrology and chemistry Vecchioli, J., Gill, H.E. and Lang, S. M., 1962. Hydrologic role of groundwater and seasonal ponds in the Atlantic Coastal Plain of the Great Swamp and other marshland in Upper Passaic River in Delaware, USA. J. Hydrol., 141, 157–178. Basin. J. Amer. Water Works Assoc., 54, 695–701. Poff, N.L., Allan, J.D., Bain, M.B., Karr, J.R., Prestegaard, K.L., Verry, E.S., 1988. The hydrology of wetlands and man’s influence Richter, B.D., Sparks, R.E. and Stromberg, J.C., 1997. The on it. Symposium on the Hydrology of wetlands in temperate natural flow regime. Bioscience, 47, 769–784. and cold regions: Vol 2. Academy of Finland, Helsinki, 41–61. Price, J.S., 1992. Blanket bog in Newfoundland. Part 2. Verry, E.S. and Boelter, D.H., 1975. The influence of bogs on the Hydrological processes. J. Hydrol., 135, 103–119. distribution of streamflow from small bog upland catchments. Price, J.S. and Maloney, D.A., 1994. Hydrology of a patterned Hydrology of marsh-ridden areas, Proc. of the Minsk Symp. bog-fen complex in Southeastern Labrador, Canada. Nord. (June, 1972), International Association of Hydrological Sciences Hydrol., 25, 313–330. UNECSO/IAHS, Paris. 469–478. Raisin, G., Bartley, J. and Croome, R., 1999. Groundwater Verry, E.S. and Boelter, D.H., 1978. Peatland hydrology. In: Amer. influence on the water balance and nutrient budget of a small Wat. Resourc. Assoc. Wetland functions and values: the state natural wetland in North Eastern Victoria, Australia. Ecol. Eng., of our understanding. Amer. Water Resour. Assoc, New York. 12, 133–147. 389–402. Riekirk, H. and Korhnak, L.V., 2000. The hydrology of Cypress Verry, E.S. and Timmons, D.R., 1982. Waterborne nutrient flow wetlands in Florida pine flatwoods. Wetlands, 20, 448–460. through an upland-peatland watershed in Minnesota. Ecology, Riggs, H.C., 1964. The base-flow recession as an indicator of 63, 1456–1467. groundwater. Symposium on Surface Waters, Proceedings of Waddington, J.M., Roulet, N.T. and Hill, A.R., 1993. Runoff the General Assembly at Berkeley of I.U.G.G., IAHS Publ. no. mechanisms in a forested groundwater discharge wetland. J. 63, 352–363. Hydrol., 147, 37–60. Robertson, S.B., 1987. Hydrology of Arctic Wetlands. Proc. Nat. Walton, R., Chapman, R.S. and Davis, J.E., 1996. Development Wetland Symp: Wetland Hydrology. Assoc. of State Wetland and application of the wetlands dynamic water budget model. Managers Inc., Chicago. 262–269. Wetlands, 16, 347–357. Robinson, M., Gannon, B. and Schuch, M., 1991. A comparison Wharton, C.H., 1970. The Southern River Swamp - a Multiple- of the hydrology of moorland under natural conditions, use environment. Bureau of Business and Economic Research, agricultural use and forestry. Hydrolog. Sci. J., 36, 565–577. School of Business Administration, Georgia State University. Romanov, V.V., 1968. Hydrophysics of bogs. Israel Program for Wheeler, B.D., 1984.. British Fens: a review. In: European Mires, Scientific Translations, Jerusalem. P.D. Moore, (Ed.). Academic Press, London, UK. 237–281 Roulet, N.T. and Woo, M.K., 1986. Hydrology of a wetland in the Wheeler, B.D. and Shaw, S., 2000. A wetland framework for impact continuous permafrost region. J. Hydrol., 89, 73–91. assessment at statutory sites in Eastern England. Technical Sander, J.E., 1976. An electric analogue approach to bog Report W6-068/TR1. Environment Agency, Bristol, UK. hydrology. Ground Water, 14, 30–35. Wilcox, D.A., Shedlock, R.J. and Hendrickson, W.H., 1986. Sellars, C. D., 1981. A floodplain storage model used to determine Hydrology, water chemistry and ecological conditions in the evaporation losses in the Upper Yobe River, Northern Nigeria. raised mound of Cowles Bog. J .Ecol., 74, 1103–1117. J. Hydrol., 52, 257–268. Williams, R.E., 1968. Flow of groundwater adjacent to small, Serban, P., Stanescu, V.A. and Simota, M., 1988. Contributions to closed basins in glacial till. Water Resour. Res., 4, 777–783. the study of peatlands influence on maximum flow. Symposium Wilson, B.H. and Dincer, T., 1976. An introduction to the on the Hydrology of wetlands in temperate and cold regions: hydrology and hydrography of the Okavango Delta. Proc. Symp. Vol 1. Academy of Finland, Helsinki, 92–99. on the Okavango Delta and its future utilisation, Botswana Seyhan, E., Hope, A.S. and Schulze, R.E., 1983. Estimation of Society, Gaborone, 33–48. streamflow loss by evapotranspiration from a riparian zone. S. Wilson, T.V. and Wiser, E.H., 1974. Groundwater-baseflow Afr. J. Sci., 79, 88–90. relationships and baseflow predictions from groundwater levels Sharma, T.C., 1984. Some hydrologic characteristics of the on piedmont watersheds. Trans. Amer. Soc. Civ. Engrs, 269– Zambian headwaters. Zambian J. Sci. Technol., 7, 12–21. 279. Sharma, T.C., 1988. An evaluation of evapotranspiration in tropical Winner, M.D. and Simmons, C.E., 1977. Hydrology of the central Africa. Hydrolog. Sci. J., 33, 31–40. Creeping Swamp watershed, North Carolina, with reference to Shedlock, R.J., Wilcox, D.A., Thompson, T.A. and Cohen, D. A., potential effects of stream channelization. U.S.G.S./WRI-77/ 1993. Interactions between groundwater and wetlands, southern 26. shore of Lake Michigan, USA. J. Hydrol., 141, 127–156. Wolski, A., 2002. Hydrological processes in the Okavango Shjeflo, J.B., 1968. Evapotranspiration and the water budget of wetland, Botswana. Proc. EGS. Nice, April 2002. prairie potholes in North Dakota. Geol. Surv. Prof. Pap. 585- Woo, M.K. and Heron, R., 1987. Effects of forests on wetland B, United States Government Printing Office, Washington. runoff during spring. In: Forest Hydrology and Watershed Shiklimanov, I.A. and Novikov, S.M., 1988. Drainage effect on Management. R.H. Swanson (Ed.), Proc. of the Vancouver the environment. Symposium on the Hydrology of wetlands in Symposium, IAHS Publ. no. 167, 297–307. temperate and cold regions: Vol 2. Academy of Finland, Woo, M.K. and Rowsell, R.D., 1993. Hydrology of a prairie Helsinki, 66–71. slough. J. Hydrol., 146 175–207. Siegel, D.I., 1983. Groundwater and the evolution of patterned Woo, M.K. and Winter, T.C., 1993. The role of permafrost and mires, glacial Lake Agassiz peatlands, Northern Minnesota. J. seasonal frost in the hydrology of northern wetlands in North Ecol., 71, 913–921. America. J. Hydrol., 141, 5–32.

372 The role of wetlands in the hydrological cycle

Zivert, A.A., Rieksts, I.A. and Skinkis, C.M., 1975. Investigation of runoff in drainage outlets and subsurface drained soils in the Latvian SSR. Hydrology of marsh-ridden areas, Proc. of the Minsk Symp (June, 1972), International Association of Hydrological Sciences, UNESCO/IAHS, Paris. 117–128.

373 Andy Bullock and Mike Acreman

summary DPFV: - DPAE: + . MAF: -FPLM: FEV: + DPRR: + DPFV: - DPAE: + GDS: = DPFV: - FVa: - MAAE: + DPFV: - DPFV: + . MAF: DPFV: . + FPLM: FTTP: + + FRR: WPFVa: + GDS: X GDS: =

... Summary of functionalSummary statement evapotranspiration summer high ... by DPAE: little have : swamplands effect on the totalMAF flow floods decreases the downstream the swamp FPLM: seasonal runoffFEV: is greater than that of the upland (p.699-700) Function recession River (p.359). of the non-wetland New in baseflow is an area of discharge the for swamp the regionalGDS: groundwater (p.body B179) vegetation (p.254) out 14 milliards is flow (p.731-2) lost of in theMAAE: swamps both zero eventually flow areas from DPFV: becomes higher occur peaks for much the undrainedFPLM: area the undrainedFTTP: area sooner than flows the drained area afterFRR: flood peaks, the drained area is still dischargingat water a faster rate in sustained the uniform drained are more flows areaWPFVa: (p.814-6) (p.257). (p.257). annual runoff. groundwater than twice as (p.27) much groundwater system (p. 309) system groundwater (p.309) the table water reacts GDS: quite independently the regional from surroundingsoil mineral from groundwater recharges GDS: the bog recharged during the was period “Groundwater (p.60) of study” AGR: AGR+ gw GW GW Category of study Comp Comp Comp SEH depletion of flow accounted phraetophytic can be 70% for by DPFV: SEH SEH phreatophytes in DPFV: the at valley by least diminished flow 20% phreatophytes (p.259) of river depleted DPFV: flow 100% - DPFV: V V V GW GW GW inference inference Multiple LTH basins more lake have or DPFV: having areas wetland inexcess of 5% Local term term Local of Basis marsh GW/S GW/S marsh Swamp, In-out LTH is the of baseflow input reduced to 75% DPFV: bog, Swamp, General Wetland Wetland type Comp General valley Swamp RiverGW/S Comp Paired pothole LTH Prairie GW/D a steep with a flat of comparison Haw, recession DPRR: for the swampy GW/S Comp marsh Swamp, In-out bog WB Perched SW/S evapotranspiration summer causes a significant reduction DPFV/DPAE: New Jersey, USA Minnesota, USA province) Tennessee, USA Saskatchewan, Canada Saskatchewan, Canada USA USA . et et al . (1962) al (1967) Author Country (state, Author Country Hurst (1933) Sudan Vecchioli FP Comp Comp Sudd valley (1964)Riggs Carolina, N. valley Meyboom In-Out (1964) River LTH FP River discharge little; varies very swamp FVa: fluctuations are rapidly damped FP Meyboom (1966) Miller (1965) Jersey, New Ackroyd (1967) Bay Comp Bog Minnesota, GW/S (1968)Burke Ireland SW/S Peat Drained WB drained and undrained from outflow is area the same MAF: Annex 1 FUNCTIONS QUANTITY REVIEW OF WETLAND WATER GLOBAL

374 The role of wetlands in the hydrological cycle

MAAE: . . MAF: FVa: - DPFD: - . FVa: -FPLM: -FRR: WPF: + AGR: - DPFV: - .FPHM: AGR: - DPFV: - .FPHM: AGR: - WPF: + DPFV: - .FPHM: WPF: + DPFV: - -FPLM: -FTTP: . FVa: DPFV: + WPGR: X DPGR: = DPGR: X GDS: = GDS: X GDS: = AGR: = FVa: bogs were notFVa: bogs were effective regulators as streamflow that out suggest recessions long-drawn and flows peak low FRR: FPLM/ do store runoff short-term bogs (p.101)the the aquifer; recharges amount small a off in runs only and spring water (Novitski, fall p. 147) winter and is in reduced summer, flow thus base 5-100 yrs) = (T variability of flood peaks spring to runoff is recharge groundwater greater and AGR/WPF/DPFV: and of lake percentage larger in a with basins lower (and baseflows) p.145-9) (Novitski, area wetland areas redistribution the causes bogs to become of highmoor drainage FVa: (p.232-3) marked. more 20 yrs) = (T variability of flood peaks results in basins of storage in reduced percentage large AGR/DPFV: p. (Novitski, 145-8) baseflow reduced consequently and recharge 5-100 yrs) = (T variability of flood peaks large for with basins lower are series annual minimum WPF/DPFV: p.149) (Novitski, wetlands and of lakes percentages influence damping a suggests Yellow 24 hours the behind lag of the Alcovy peaks FTTP: minor many and smooth are durtion curves flow Alcovy FVa: fluctuations for shown the are missing. Yellow It is likely that the Alcovy (alluvial) the the influence floodplain beneath aquifer strongly does variability flow of base are flows larger, its low 36% area drains an the although Yellow DPFV: close to those of the suggesting Alcovy, possible some influence of the (p.15-18). flow on base swamp months when the potholes were frozen (p.B48) frozen potholes the were when months 39 do not recharge and Recharge’ ’Slow ’Slow 10 as sloughs’, discharging classified ’Fast as 14 are GDS: (p. 50 do not discharge. 12-14) sloughs’, Discharging groundwater mound (p.782) mound groundwater sinks, others a as groundwater as behave marshes some GDS/AGR: GW WB Comp that took place no seepage during the assumed it winter was WPGR: Chem 10 as 76 sloughs among 27 Recharge’, are DPGR: classified as ’Fast GW GW GW Multiple LTH basin FPHM: storage is statistically insignificant in explaining the ponds SW/S SW/S Peat bog Slough SW/D Comp Same LTH General not storage DPFD: was available to sustain flow summer storage Basin and Multiple LTH Lakes General area, more wetland and lake large with in basins DPFV: WPF/AGR/ General Basin storage Multiple LTH basin FPHM: storage is statistically insignificant in explaining the Former USSR USSR Former SW/D USA Dakota, N. Bogs SW/D Illinois, USA Prairie pothole GW/D Same Comp USA WB Marsh that of unbogged approaches runoff and evaporation bog MAAE/MAF: Comp Canada Wisconsin, USA New York, USA Delaware, USA Maryland, Virginia, USA General Basin storage USA Georgia, Multiple FP LTH basin FPHM: storage is statistically insignificant in explaining the Swamp Paired LTH hydrographs Yellow and (swamp) Alcovy of comparison a FPLM: Romanov Romanov (1968) Shjeflo (1968) Williams (1968) (1969) Bay Minnesota, Freeze (1969) Saskatchewan, Campbell & Drecher (1970) in Novitski (1985) Darmer (1970) in Novitski (1985) Forest & Walker (1970) in Novitski (1985) Nuckles (1970) in Novitski (1985) Wharton (1970)

375 Andy Bullock and Mike Acreman GDS: = AGR: = AGR+ DPAE: - GDS: = FPHM: - - FPHM: - FPLM: - DPFV: + FEV: .MAF: WPF: + - FRR: - MAAE: - DPFD: DPRR: + - DPFV: DPAE: + .MAF: .MAF: ng andng little further retention takes ss accounts, on average, for 60% or 60% for accounts, onaverage, ss table (p.A82) (p.A82) table elevations on glacial till. (p.D4-D5) more of total water loss in sloughs less than 1.0 acres in size and not not and size in acres 1.0 than less sloughs in loss water total of more (p.259) acre” 1 than larger sloughs in 30-35% than more DPAE: “Reductionin evaporation due loss (is to) of sheltering the effect (p279) vegetation” emergent and marginal and topography seepage inflow. (pD4-D5)seepage peaks (T = 2-100 = (T thepeaks yrs); higherthe term, the storage lower flood (p.144-5) peaks. p.126); (Bardecki, basin undrained and drained FEV: saturatedare materials the in spri place. (p.17) runoff higher a higher dambopercentageWPF: area, a of surface from volume occurs FRR: duration ofsurface runoff as compared with a non-swampy area is dambo resistance by delayed evapotranspirationMAAE: woodland by istimes three higher than that from dambos the transitive than earlier from the dambo ceases from DPFD: flow base region containing a catchment dambo 10% from DPRR: steeper are recessions (239-248) dambo 5% with compared but water through it the of some potential is baseflow lost to (p.274) evapotranspiration (p.301) same the catchment (p.302) swampy the ponds the water GDS: in of "outcrops" prairie are potholes, in effect, DPFV:there is no evidencewetland the of sustaining (p.41) baseflow DPFV:. GW V WB WB “Shorelinelo AGR: related water Chem Ponds GDS: elevations, at lower on subjectoutwash, to were greater Comp Chem loss inwater ponds accounted for some seepage at higher AGR: Comp

GW E GW GW V GW Comp Drained LTH increased FPLM: due is to a peak flow drainage of study comparative in a Comp Comp wetland pothole pothole General Basin storage Multiple General General LTH FPHM: basin is storage significant in explaining variabilityflood in Pond SW/S Comp FP Floodplain In-out LTH contribute to fail zone (floodplain) lower the does only not DPFV/DPAE: Wisconsin, Wisconsin, USA USA Dakota, N. & Manitoba, Canada USA Dakota, N. GW/D New Hampshire, Prairie USA USA Illinois, GW/S N.Dakota, USA Bog SW/D Prairie pothole Comp In-out Zambia WB GW/S baseflow as basin the left no groundwater DPFV: Dambo Same S. Carolina, USA CCM dambos the of size the of independent is runoff total MAF: USSR European SW/S bogs Raised Paired WB was basins river (non-swamp) the from and swamp the from runoff MAF: et (1972) (1972) Conger Conger (1971) in Novitski (1985) (1971) Kloet in Bardecki (1987) (1971) Millar Canada GW/S Eisenlohr (1972) Comp Prairie Hall et al. (1972) McComas pothole al. Stewart & Kantrud (1972) Prairie GW/S Perry Balek & (1973) & Wilson (1974) Wiser Bavina (1975) FP bogs Valley Paired WB from runoff with agreement general in is swamp the from runoff : MAF

376 The role of wetlands in the hydrological cycle MAF: - MAF: + MAAE: + WPF: - WPF: DPFV: - + FVa: - MAF: - FVa: FEV: - . AGR: + FPLM: DPFV: - + MAAE: - MAF: . FVa: . AGR: - FVa: - FPLM: DPFV: + = AGR: = GDS: DPFV: - + FPLM: . FPLM: . FTTP: + FVa: - MAF: . MAF: + MAAE: - MAF: - WPF: DPFV: - MAF: + + MAF: + WPF: . WPF: - WPF: + FPLM: . FPLM: - FPLM: undrained area. Flow was much more uniform and did not show the the show not did and uniform more much was Flow area. undrained sharp peaks evident in the undrained area occur, may albeit seepage some AGR: small, but both peat and the subsoil permeability low extremely have and in frequency reduced be will floods drainage, after FPLM/DPFV: short-term in the increased be will streams of flow summer and amount (p.176) laterally moves outflow seepage the of most downward, vertically moves (p.309) (p.38-40) recharge groundwater of sources as decrease in evapotranspiration WPF: spring either flows increase or decrease DPFV: increase low considerably flows andminimum summer increases, flow to contribution groundwater the of proportion the FVa: (p.466) runoff river of distribution the improving runoffwith respect to mineral soils FVa: there is no causal relations between the runoff steady and thewater (p.359) peat of storage dischargesthe increased maximum and the decreased (p.514) minimum other in on 7 basins; 17-30% by decreased discharges maximum FPLM: basins no significant change occurred the of timing the in observed were changes no significant : FTTP peak the of date in the or flood, snowmelt 10 to of flow spring of decrease by characterised were 6 basins FVa: to 60% 20 increased flow autumn and summer 30%; 7 basins other the On 20%. 10 to by increased 9 basins of MAF MAF: there nowas significant change (p.424-6). reclamation period to compared as in runoff, increase 20% a show results MAF/WPF/DPFV: in runoff, the in increases were there period... pre-reclamation the summer and autumn (p.59) WPF: decrease in spring flows is generally found but cases are are cases but found generally is flows spring in decrease WPF: increase to or tends unchanged is flow the where encountered FPLM : drainage doesnot affect the discharge,always maximum (p.442) or increase decrease either may it although seepage of portion small very a that evidence is there although AGR: serve also may and groundwater by supplied be may swamps AGR/GDS: GW GW Comp Comp GW GW Comp Prairie Pothole

USSR USSR General Peat Drained LTH Germany a to due increased is runoff annual drainage after initially MAF/MAAE: SW/S N. Dakota, USA GW/D Peat Latvia Estonia Same General Swamp Comp Byelarus GW/S WB GW/S Marsh Byelorussia MAAE/MAF: there is higher evaporation peat from and reduction of bogs Fen SW/S Drained LTH Drained Marsh WB FVa/FPLM/DPFV: river variability flow increased following drainage as (p.489) 92mm by increases bogs fen drained from runoff annual MAF: Drained - MAF: LTH DPFV:the discharge minimum increased by 30-150% Poland N.E. GW/S bog Peat Drained WB pre- the with compared as 15% about by decreased evaporation MAAE: Ukraine Ukraine FP Marsh Drained LTH drainage after decrease to tends runoff MAF: et (1975) (1975) Bulavko & (1975) Drozd (1975) Burke Ireland SW/S Eggelsmann peat Blanket (1975) Drained WB Eisenlohr (1975) the than greater 60% was runoff area drained the MAF/FVa/FEV: Glazacheva (1975) Hommik & Madissoon (1975) Kiselev (1975) Klueva (1975) Moklyak al. Mikulski & Lesniak (1975)

377 Andy Bullock and Mike Acreman DPFV: - DPFV: DPAE: + AGR: - - FRR: - FPLM: + FVa: MAAE: + MAAE: -MAF: - FPLM: - DPFV: - FPLM: - FPHM: + MAF: WPVa: - WPF: + FTTP: + - FPLM: - DPFV: - FRR: + MAAE: -MAF: FVa: . FVa: - FPLM: . FPHM: - FRR: - FRR: AGR: X + MAAE: . FVa: - FPLM: . FPHM: - FRR: + FVa: WPF: + - DPFV: DPAE: + GDS: = is at the expense of flow and flow deep peatland expense the is at of seepage; does not sustain water stored releasing slowly by months summer dry during streamflow have hydrographs Storm peatland. by modified are stormflows FRR: curves recession out long-drawn FPLM: peatland flow does rates of reducepeak the streamflow of distribution even an maintain fens nor bogs neither FVa: (p.14-18) runoff FPLM: an accelerationcausedflowdrainage the of by network led to an runoff inincrease maximum DPFV: runoff for boththe increased minimum winter and summer (p.523) markedly on the a flood shapehydrograph of is the attenuation the of peak discharge (p.9) peat in uniform more is discharge flood of hydrograph The soils. mineral than in mineral soils (p.121) theFTTP: the flood drained from peatland began earlier and lasted longer FPLM: peak flow of the former remainedlower was summer dry the during peatland drained the from runoff DPFV: greater (p.84- longer lasted and earlier began peat drained the from flood FRR: 5) evapotranspirationthe (p.36). losses FVa: the perched bog has no regulating effect effect no regulating has bog perched the FVa: peaks storm individual reduce does bog the FPLM: independent are FPHM: peaks maximum bog the of (p.472) flow storm of release the delays bog the FRR: June early until prolonged is runoff surface the of duration the FRR: (p.159) virtually no vertical movement vegetationMAAE: is pump, actingas a removing the water from water (p.128-135) transpiration via table FVa:the groundwater bogno has regulating effect peaks flow storm reduce does bog the FPLM: independent are peaks FPHM:of bog the maximum (p.472) flow storm of release the delays bog the FRR: role is to chief seasonal a significant superimpose FVa: the bog’s discharge on fluctuation during periods water WPF: wet the excess bog releases periods dry during supplies available depletes bog the DPFV/DPAE: evapotranspiration through groundwaterfrom (p.35) the water wetlandGDS: receives table the between and water the clays Floridan AGR: aquiferallow GW SEH CCM SEH /CCM WB evapotranspiration fall early and summer spring, late DPFV/DPAE/AGR: GW Same Comp Same Comp swamp swamp bog GW/S Lake-filled bog Same LTH, LTH, Same bog Lake-filledGW/S Bog GW/S WB In-out peat Perched SW/S Finland SW/S Peat Drained Minnesota, LTH USA in evapotranspiration decrease MAAE/MAF: led to in an increase total USSR Finland GW/S SW/S bog Fen Peat Same USA WB Drained than greater 40% to 20 is flow drainage bogs fen in MAF/WPVa: WB Botswana considerably WPF: caused on peak flow was lower the drained peatland FP Lake Northern States, USA Delta In-out WB MAAE/MAF: outflow in the Boteti amounts to2% onlyinflow ofdue to

et al. Mustonen & & Mustonen (1975) Seuna LTH, Same (1975) NERC UK (1975) Smith bog USA Florida, FP FP & Verry Boelter (1975) Lake-filled Cypress Floodplain SW/S In-out SEH Zivert (1975) floodplain large a by induced change important most the FPLM/FPHM: Heikuranen (1976) (1976) Sander Minnesota, & Wilson Dincer (1976) (1977) Balek Zambia Boelter & (1977) Verry GW/S Dambo Same WB/

378 The role of wetlands in the hydrological cycle FVa: + + FVa: + WPF: DPFV: - DPAE: + - FVa: WPAE: - + WPF: DPAE: + DPFV: - DPGR: = - FPLM: DPFV: - MAF: . - FPLM: + WPF: AGR: - DPFV: - - FVa: - FPLM: DPFV: - DPGR: - GDS: = FPHM: . FPHM: AGR: X GDS: = DPFV: - - FEV: . FEV: DPFV: + WPAE: - + WPF: DPAE: + DPFV: - GDS: = opposite by releasing excess water more quickly than mineral aquifers aquifers mineral than quickly more water excess releasing by opposite by water more losing and precipitation high of periods during 15-16) (p. periods dry during evapotranspiration regimes (p.472) (p.472) regimes spring WPAE: evapotranspiration is depressed relative tonon-wetland WPF: thewetlandresponsible was for high springflows areas to non-wetland high relative are rates fall DPAE: DPFV:baseflow greatly was depressed (p.336-8) groundwater recharges swamp the summer during DPGR: (p.53) change not would runoff Total increase. flows low lake and wetland much with basins in occurs runoff spring more WPF: lessAGR/DPFV: groundwater recharge (and baseflow) occursin basins (p.384-6) and wetland lake much with flow peak the reduce does peat FPLM: evapotranspiration of expense is at the summer peat DPFV/DPGR: (p.398) recharge or streamflow 31). (p. large quite is bedrock the from discharge effect was seen on any other storm occurrences other storm seen on any was effect DPFV:maintenance flow can significant be very (p.77-8,90) WPF: thewetlandresponsible was for high springflows areas torelative non-wetland high are rates fall DPAE: DPFV: baseflow during the period flow low greatly was depressed body regional the groundwater from water receives the wetland GDS: (p.336-338) variability of flood peaks (T = 5-100 yrs) (p.145) (p.145) yrs) 5-100 = (T peaks flood of variability are considered losses zero Groundwater less estimated to than the flow minimum reduced wetland DPFV: the (p.46) flow base WB, LTH WB, LTH LTH WB, spring WPAE: evapotranspiration is depressed relative tonon-wetland WB do the may fen the flow, regulating instead of FVa/WPF/DPFV/DPAE: WB the GDS: of volume (ground-)water annually entering by the swamp GW GW Comp Drained Drained CCM water of stability greater to contribute swamps cypress of retention FVa: same Drained LTH Multiple increase; exceedance-percentile) 5 (> flows higher FPLM/DPFV/MAF: LTH and lake wetland much basins in with lower 80% be may flows FPLM: Same Same peat fen peat fen Forest swamp Same WB individual an of event. No is 7.8% swamp the retained by FEV: water swamp swamp swamp lake

General General storage Basin Multiple GW/S LTH Wetland thein insignificant explaining is statistically storage basin FPHM: Same WB Paired, Peat GW/S till.glacial the local for is discharge a point of the wetland AGR/GDS: FP Floodplain and Wetland General GW/S Fen Same WB (p.398) peat the through discharge not does fen GW/S the AGR: x AGR: Illinois, USA USA Illinois, FP Illinois, USA GW/S Swamp Comp Pennsylvania, Pennsylvania, USA Minnesota, USA Florida, USA FP Massachusetts, Cypress USA Carolina, N. USA Wisconsin, USA Minnesota, USA

. et al et al. et al. (1977) (1977) (1979) GW/S Groundwater Groundwater GW/S (1977) Flippo in Novitski (1985) Hickok Littlejohn Paired, (1977) Mitsch wetland O’Brien (1977) Muck SW/S Winner & Simmons (1977) Novitski (1978) & Verry Boelter (1978) McKay SW/S Peat Same WB FVa: peatsdonot regulate one from season flow toanother (1977) (1977)

379 Andy Bullock and Mike Acreman MAF: - - FPHM: DPFV: - FPHM: - FPHM: DPFV: . MAAE: + MAF: - MAAE: + MAF: - - FPLM: DPFV: - DPAE: + MAF: . - FPLM: FTTP: + MAF: . DPFV: + MAF: - DPFV: + AGR: = - FPLM: DPFV: + . WPF: MAAE: + - FPLM: DPFV: + WPF: + MAAE: . - FPLM: DPFV: . . WPF: MAAE: + AGR: = FEV: + + FEV: WPF: . WPF: - FPLM: AGR: = the increase in maximum flow, and 70% of the of increase is in spring flow and 70% flow, increasethein maximum (p.13) drainage to increased due DPFV: dambo catchments are not significantly distinguishable from from distinguishable significantly not are catchments dambo DPFV: Q75 for neighbours unaffected increases evaporation a with dambo of presence MAAE/MAF: annual (p.58)corresponding yield in average decrease ... inFPLM: effect reducing an flood peaks flows base increasing on effect ... some DPFV: runoff time spring increases ... WPF: (p.19-20) ET on effect no ... MAAE: ... inFPLM: effect reducing an flood peaks flows base increasing on effect ... no DPFV: runoff time spring increasing on effect no ... WPF: ... ineffect increasing an ET MAAE: (p.19-20) occurs recharge some AGR: every 1% of dambo (p.16) (p.16) dambo of 1% every none show Swamp Van wetland the raised therewetlands usually is little from discharge after DPFV/DPAE: evapotranspiration of because June is equal (p.90-3) nearly catchments the two runoff from MAF: (p.115) total flow in little difference was there MAF: periglacialcharacterised by deposits(p.69). and peat contribute losses of 10% season. dry the into continue to flooding causes (p. 267) groundwater to regional peaks flood reducing in effect ... an FPLM: flows base increasing on effect ... some DPFV: runoff time spring increasing on effect no ... WPF: (p19-.20) ET increasing in effect some ... MAAE: from saturation overland flow on the floodplain (p.54) (p.54) floodplain on the flow overland saturation from than originating from the wetlands) (p.359) (p.359) wetlands) the from originating than (p.168,173) floodplains on occurs recharge significant AGR: LTH all(rather of flood component peaks the major was groundwater WPF: LTH flooding floodplains FPLM: downstream ameliorate WB FEV:the dominantand rapid hydrograph response essentially comes CCM Storage MAF. of 70% are Yobe Upper in the losses MAF/DPFV/AGR: WC GW GW ET Kettle hole In-out WB (p.522)recharge of absence the an is bog characterised by GDS: X GDS: SW/D SW/D GW/S Wetland Comp Comp Floodplain FP GW/S Pocosin GW/S Drained WB Pocosin while floods five show Canal Albemarle the from hydrographs FPLM: Drained WB earlier are higher and sites peaks ondeveloped FPLM/FTTP: SW/D wetland SW/D Same WB ... has wetland depression surface-water A N. Dakota, USA USA Dakota, N. GW/D Sloughs Drained TS of 36% flow, in increase the of 50% approximately MAF/FPHM/DPFV: Malawi Malawi FP Dambo Multiple LTH storage floodplain of lot a provides dambo FPHM: Massachusetts, Massachusetts, USA Malawi Massachusetts, USA GW/S Mississippi, USA Dambo Multiple LTH USA for 6.4mm by is reduced volume runoff annual average MAAE/MAF: N. Carolina USA Comp UK Wales, Floodplain FP Brazil GW/S Peat Wisconsin, USA Same SEH areas yields prevailed, headwater two excepting low very DPFV:

. et al. et al (1981) (1980) Drayton Drayton Hemond (1980) Hill Kidd & (1980) O’Brien (1980) Bedinger (1981) Brun (1981) Daniel Carolina, N. Gilliam & Skaggs (1981) Newson (1981) Nortcliff & Thornes (1981) Sellars (1981) Nigeria Novitski (1982) FP Floodplain Comp SW/S wetland SW/S Same GW/D WB wetland GW/D Same ... has wetland slope surface-water A WB ... has wetland depression ground-water A

380 The role of wetlands in the hydrological cycle DPAE: + MAAE: + FPLM: - - FPLM: DPFV: . + WPF: MAAE: + - FPLM: MAF: . + FEV: . AGR: DPAE: + MAAE: - - FEV: DPFV: - DPAE: + AGR: = AGR: X WPGR: = AGR: = MAF: - - FPHM: AGR: = GDS: = AGR: X + FPLM: + FEV: WPAE: + - WPF: AGR: + , while runoff attained 80% of input under rainfall of 30mm 30mm of rainfall under input of 80% attained runoff while , -1 on hydromorphic soils -1 evaporative losses during the day, which could not be detected when the when not could detected which be during losses day, the evaporative macrophyte growth (p.57) minimal was higher than from non-flooded areas. (p.12-21) (p.12-21) areas. non-flooded from than higher FPLM: an effect in reducing flood in reducing peaks effect an FPLM: flows base increasing on effect no DPFV: runoff in increasing spring time effect an WPF: (p.19-20)increasing inET effect some MAAE: (p.16) area or lake no with basin a in than area upland the as same much flow transmit can bog the periods, table water high during FEV: soil mineral the than quicker and peat well-decomposed of conductivities hydraulic because AGR: periodsover long rates are probably tillglacial similar, seepage are (p.1461) similar 88) (p. day the during zone riparian the in losses evapotranspirational wooded from 760mm and interfluve shallow from 692mm with compared interfluve there is responses less because flashy more show FEV: hydrographs retention water. for of temporary area dambo evapotranspiration dambo high results inin DPFV/DPAE: a decrease (p.36). flow river of cessation and rate flow artesian is aquifer underlying the as percolation deep little is there Cary 80). (p. it until groundwater and runoff incoming and rain retain wetlands DPFV: (p.839) percolates or evaporates 41% of 100-year return period (p.45) flow Precipitationadjacent fens. are thezones not doesthe on the enter fens (p. 918) system groundwater ferrallitic soils from than is lower soils hydromorphic/gley of rainfall under occurs runoff no soils, forest drained freely on FEV: hr 120mm h are there floodsgreater where during severe are far losses WPAE/WPF: totalof the flood 30% floodplains. almost represents In Mauritania, this volume into disappears itsstream floodplain, a alluvial when water the AGR: (p.244-257) replenished be may table evaporation MAAE: floodedfrom areas on the Flats is considerably ET WB Austin At groundwater. the recharges 2 Dome Sewage usually AGR: CCM raised in dischargepeats are the and zones bogs, the recharge AGR: LTH by caused were hydrographs in rhythms diurnal distinct DPAE: ET GW GW Multiple LTH and wetland lake 40% basin with in a lower 80% are peaks flood FPLM: Multiple Multiple LTH and flow period return 2-yr of 72% store depressions the MAF/FPHM: Comp Same Comp FPLM: minimum rainfall requiredto producerunoff from lake lake Shallow Shallow depressions Raised bogs Fens soilgley SW/S SW/S Peat Same WB the nearly or yield, water to precipitation its of 36% converts peat MAF: FP GW/S Marsh Same LTH greater with fluctuations diurnal exhibit hydrographs recession DPAE: GW/D Peat bog In-out Chem intogroundwater locally moving are waters bog WPGR: Minnesota, Minnesota, USA Zealand New GW/S N. Dakota, USA SW/D Macrophytes South Natal, Comp Africa USA Malawi GW/S Dambo USA Florida, GW/S Same Michigan, S.W. Comp USA domes Cypress Comp Same WB FP Zambia Floodplain Hydromorphic/ is 640mm dambos losses annual from actual evaporation MAAE: W.Africa General

et al. al. et et al. (1983) (1983) General Wetland and and Wetland General & Verry Timmons (1982) GW/S Howard- wetland GW/S Williams Same (1983) Ludden WB Seyhan ... has wetland slope groundwater A (1983) Siegel Minnesota, Smith- Carrington (1983) Heimburg (1984) Keough & (1984) Pippen Sharma (1984) Dubreuil (1985) (1983) (1983)

381 Andy Bullock and Mike Acreman FPLM: . FPLM: - FPLM: MAF: . . FPLM: DPFV: . - FPHM: + FEV: DPFV: - DPFV: + - FPHM: DPFV: . AGR: = GDS: = DPFV: - DPAE: + . FVa: DPFV: - AGR: = DPAE: + - FPLM: + WPF: DPFV: - + FVa: + FPLM: DPFV: - + FPLM: AGR: X . FPLM: GDS: = negligible. main-stem Downstream wetlands more were effective in (p.114) flooding downstream reducing (p.127) found was drainage to attributable flow in change (p.111) river wetland Blackstone lowthe adjacent 70% of total annualrunoff is quickflow but removed, decreased was vegetation after increased DPFV:flows low draining. after most the probably is flows peak large of frequency increased FPMH: important impact of drainage (p.471-3) works (p.267) streams groundwater flow away from the peat mound mound peat the from away flow groundwater (p.1111-3) deduced is peat into marl through seepage GDS: and not lateral runoff. Wetlands do not play an important role in in role important an play not do Wetlands runoff. lateral not and regulationstreamflow (p.89) by evaporationby (p.19) and seepage less are peaks : flood FPLM WPF: springrunoff is greater (p.151) less is baseflow DPFV: FPLM/DPFV:run-off in downstreamareas are such (p.206-8) thatthe smaller risk of becomes dryness and highwater (p.94)prior table water storm to a thata near-surface is saturated or has negligible FPLM: during snowmelt, wetland soilsdo not contribute significantly to flood storage (p.209). cover and from adjacent forested areas. Most of the runoff from the bogrunoff from Most the of areas. adjacent forested andcover from (p.303-4) flow groundwater as occurred a pattern shallow in of the table mound peat water causes a AGR: GW WB openmeltwater GDS: from bogs andfens is supplied the local by snow Comp WB DPFV/DPAE/FVa:post-spring water lossmainly due is toevaporation WC WC GW Same Same LTH Multiple DPFV: duringseason,dry the retain water is which lost surface swamps LTH In basinswith large percentages of lakes and wetlands... Same LTH FPLM: runoff can be related catchment volume storm the to of area the In-out WB contribution the AGR: wetlands of Alaskan to groundwaterprobably is swamps andswamps bolis lake Raised bog Drained WB heath FVa: run-off of the predrained extreme more bog was wetland General Wetland and and Wetland General FP GW/S Peat Wetland Comp With-out CCM General is mitigation flood for wetland upstream an of worth the FPLM: General FP Drained Floodplain LTH GW/S Paired MAF/ FPLM/DPFV: neither strong evidence norclear suggestions of any LTH Pakihi wetland Drained tocompared low floods extremely the are in Charles FPHM: maximum WB GW/S FEV: naturalundrained wetlandshighly are responsive to rainfall. Over Bogs and fens Comp Sierra Leone Sierra FP and Northern States, Eastern USA Inland valley Germany SW/S UK England, SW/S Massachusetts, USA Saturated NW Territories, Canada USA Indiana, GW/S Ontario, S.W. Canada fen Peat USA Comp Alaska, USA General Island, South General Zealand New USA Alaska, N. Ontario, General Canada General Same LTH DPFV: wetlands contribute little to the budget mid-summer tundra of

et al. Millington (1985) Novitski (1985) & Baden Eggelsmann (1986) Gurnell & Gregory (1986) & Ogawa (1986) Male Roulet & (1986) Woo Wilcox (1986) Bardecki (1987) (1987) Doyle Massachusetts, & Ford Bedford (1987) Jackson (1987) Robertson (1987) Woo Heron & (1987)

382 The role of wetlands in the hydrological cycle DPFV: + + DPFV: + MAAE: . MAF: - DPFV: - DPFV: AGR: X FEV: - + MAAE: - MAF: + MAF: FPLM: + - DPFV: + FVa: MAF: - - MAF: AGR: X GDS: X - DPFV: FEV: - - DPFV: - MAF: MAF: - - MAF: FPLM: - FEV: + FPLM: - + DPFV: FPHM: + (p.38-9) (p.38-9) 3 m 6 groundwater levels in the bogs are always sufficiently high to provide the the provide to high sufficiently always are bogs the in levels groundwater streamsfrom these areaswith runoff (p.90) (p.24) (p.178) rainfall of 30% about is seepage upward GDS: DPFV:(p.204) increased discharges low generally period to due capacity storage low = GDS: percolation through intoby deep aquifers losses of lack there a is AGR: (p.20-1) saturated layers peat frozen 94) tropical(p.38-39) wetlands reduced is MAF when cases fall to tend maxima spring high FPLM: DPFV: drainage runoff and after minimum summer tends swamps from to increase distribution flow even and uniform more as manifested is drainage FVa: over seasons (p.69-71) x 10 (p.427) measure to small too is wetlands from discharge Groundwater because months summer during reduced generally is streamflow DPFV: of high evapotranspiration water increase in to both appears extraction peat fens and bogs MAF: (p.114-5) term short the over yield outflow rates(p.490) mire (p.81) substantial experienced sub-basin disturbed the in regime flow DPFV: (p.295-6) flows in low decrease as such changes from the mineral soil not was observed (p.55)

Comp GW

GW Drained Drained CCM unmined than peatlands mined for greater is runoff FEV: bog GW/S GW/S Peat Drained CCM peak and runoff annual the increases alone mining peat MAF/FPLM: SW/S Aapa-mire GW/S Same Peat WB the from water the of runoff rapid by caused was runoff maximum FEV: Drained LTH folds five to two by increased are flows FPLM: peak GW/S GW/S Mire and peat Fen Same SEH flow - overland reservoir a like looks peat storms, large during FPHM: Poland GW/S Peat Comp Poland GW/S S.C. Sweden GW/S Carolina, North USA Mire Byelorussia SW/S Multiple LTH Bog Sweden DPFV: theprincipal differencebetween raised bogs and till is Siberia West GW/S Drained SW/S WB Peat Finnish Palsa bogs Lappland evaporation decreases MAAE: 7-10% followingreclamation drainage Same Drained Canada LTH WB Romania warm the or of months weeks in some completely ceases DPFV: flow drainage MAF: changed insignificantly MAF Africa, Zambia GW/S GW/S Peat Dambos Russia Same Paired GW/S WB LTH Swamp a ratio MAAE: ET/PET of (Penman) equal to1.5 is not surprising for FEV: runoff the in basin peat is 30-35%thanlowerincontrol the (p.93- Minnesota, Drained USA LTH Minnesota, USA some are There years. first in the MAF increases mainly drainage MAF: .

et al et et al.et et al. (1988) (1988) Brandesten Brandesten (1988) Konyha Kovrigo & Yatsukhno (1988) Kowalik Lundin (1988) Moskvin (1988) Nisula & Kuittinen (1988) (1988) Panu Newfoundland, Serban Sharma (1988) Shiklimanov & Novikov (1988) (1988) Siegel USA Alaska, FP GW/S Verry (1988) bog Brooks & Blanket (1989) Kreft Swamps Same Same CCM small. very are discharge and WB recharge wetland AGR/GDS/DPFV: 5600 to reduced is runoff annual mean the swamps, the of because MAF: (1988) (1988) (1988)

383 Andy Bullock and Mike Acreman FPLM: . . FPLM: + FPLM: AGR: X DPAE: + AGR: = MAAE: + MAAE: + MAAE: + MAAE: . MAAE: - FVa: - FVa: AGR: X AGR: = - FPLM: - DPFV: AGR: X DPAE: + - FPLM: WPGR: = -MAF: + MAAE: - FPLM: - DPFV: DPAE: + - DPFV: FPLM: - - FPLM: - FEV: + DPFV: AGR: . AGR: + + DPFV: of of 3 m 6 for the area 1 and 3.2mm d 3.2mm and -1 was estimated to be 3.5mm d 3.5mm be to estimated was 2 flood peaks. The wetlands may have a lesser ability to attenuate ability lesser have a flood wetlandsflood may The peaks. thanpeaks would upland areas. wetlands have noAGR: significant rolein groundwater recharge. (p.412) recharge to therecharge (p.418)formation Chad outsidedambos the (p.48-59) 200 km 200 inflow,the in lower insignificant, are Senegal and in the a are Okavango inflows the of proportion high very FVa:Okavango damping and variable after Sudd even less are outflows (p.54-5). through losses experiences dome infiltrationcypress (p.172- or seepage 173) 10 x 1400 provide floodplains flooded seasonally the AGR: (p.1050) flows low reduced wetlands state, pre-drained their in DPFV: DPAE: season dry evaporation approximately 50% was higherfrom the (p.153-5) dryland from than dambo (p.274) plains flood sandy wide the on losses infiltration and flows low greater evapotranspirationreduced were Peak flows losses. (p.275) higher were (p.161) disappears runoff direct and drops table FEV:increasingfloodwetland with volumes decrease DPFV:wetlands consistently (p.949) increased flows low insignificant. Seepage from the two ponds overlying permeable sand and and sand permeable overlying ponds two the from Seepage insignificant. (p.313) discharge groundwater double to enough large is gravel AGR/DPFV: seepagethe from two ponds overlying impermeable till is evaporation DPAE: of value the mean over all dambo regionsover the GW ET WB bog theand AGR: pocosin wetlands have virtually no recharge, the WB water the - output major a is evapotranspiration summer DPAE/DPFV: GW ET General Forest wetland Comp wetland Forest General SW/S Wetland In-out WB (p.225) wetland the of portion eastern the in found was recharge AGR: = AGR: Colorado, USA USA Colorado, SW/S lakes Infilled In-out LTH of magnitude the on affect substantial a have not do wetlands FPLM: Netherlands Zimbabwe GW/S GW/S Dambo Comp Same Quaking fen Same WB Africa for groundwatera focus discharge the is (p.31) fen GDS: FP USA Floodplain = GDS: S. Ontario, Canada Multiple CCM in the losses Suddand MAAE: in annual the over the half are Niger USA Illinois, General Zimbabwe Wetland GW/S USA Illinois, Drained GW/S Dambo LTH India Pond flooding. reduced wetland state, pre-drained their in FPLM: Germany Same FP WB In-out GW/S Fen GW/D Belgium small is groundwater Comp to dambo the from lost water of amount Comp total AGR: Floodplain Peat With-out CCM Drained and retention large to due decrease volumes flood FPLM/WPGR: WB MAF/MAAE/FPLM/DPFV:and drainage increased wetlands flows of Illinois, USA General Wetland Multiple LTH with FPLM: increasing decrease wetland peakflows

et et et al. et al.et (1991) (1991) obinson obinson (1989) al. (1991) (1991) al. Koerselman Koerselman (1989) Stewart (1989) Sundeen Sutcliffe & Parks (1989) (1990) Brown America, North Gehrels & Mulamoottil (1990) (1990) Hollis Nigeria Demissie al. FP & Demissie Khan (1991) Faulkner & Floodplain Lambert (1991) In-out & Hensel (1991) Miller WB Nielsen (1991) R & Boeye Verheyen (1992)

384 The role of wetlands in the hydrological cycle DPAE: + GDS: = AGR: = GDS: = AGR: = + FVa: - FVa: + MAAE: -MAF: - FPLM: -MAF: + MAAE: MAF: .MAF: . DPFV: - DPFV: . FPHM: AGR: = GDS: = - FVa: + MAF: + MAAE: -MAF: AGR: - . DPFV: GDS: = + FVa: DPAE: + - DPFV: (p.52,67) 3 m 9 ; the water budgetwater ; the the of Yaere 3 m 9 and outflow is 1.1 10 1.1 is outflow and 3 m 9 and outflow is 0.8 10 0.8 is outflow and 3 m 9 dambo margins than the central dambo and interfluve vegetation. (p.389) (p.389) vegetation. interfluve and dambo central the than margins dambo the adjacent groundwater-flow(p.176) system margins are recharge areas during periods. areas recharge wet are (p.margins 152) floodplain is inflows 3.2 10 3.2 inflows is floodplain FVa:pipe-flow and high gradients near-stream coupled the with high transmissivity produce gradient a flashy (p.103) faster A flow of stability exceptional for responsible sponge natural of evapotranspiration also decrease may and water the of increase passage (p.36). outflow of amount persistenceandvariability of annual runoff low reduce and flows low dry-season maintain not do dambos DPFV: occur they where flows in association with regolith with significant baseflow components FPHM:impact the of dambo on flood magnitude, variability and frequency is insignificant(p.349) (p.321). year the during directions considerablybroader than the actual situation. (p.322) decreases MAF swamps, without MAF: correspondinglylow runoff relative tosoils mineral groundwater. of regeneration the in important not are mires AGR: in lower 50% to 80 is groundwater deep to mires from rates Seepage (p.234-6). soils sandy than in mires occurflows during winter (p.216) of that mirrors outflow wetland of pattern seasonal FVa/DPAE/DPFV: groundwaterinflow, though amplitude because high change is greater of (p.325-6) summer the during outflow surface depletes evapotranspiration of inflow has floodplain Massenya the of budget water the MAF/MAAE: 1.7 10 by influenced strongly is ponds seasonal shallow of hydrology the GDS: DPAE: evaporation losses in August 1986 higher day-1 1 on mm are the ET GW Chem mid-October DPFV: by and negligiblewetland freeze rivers commonly Comp CCM the the zones, discharge interiorare whereas Marsh Great of AGR/GDS: GW GW WC SW/S Blanket bog FP Same WB Pantanal to of losseswas groundwater AGR:6% seepage In-out LTH condition its lose may Panatanal the of modification FVa/MAAE/MAF: SW/S Wetland Comp Wetland SW/S Indiana, USA USA Indiana, GW/S Fen Comp Zimbabwe GW/S Dambo Zimbabwe GW/S Dambo Comp Same Multiple Madagascar LTH GW/S dambos MAF: are an indiscrimatoryin factor determining the volume, Indonesia Peat FP Canada S. R., Paraguay Same Floodplain America WB With-out CCM Germany upward and downward between vary aquifers between fluxes AGR/GDS: is swamps without levels river of distribution frequency the FVa: SW/S Mires U.K. England, GW/S Paired Fen WB high characterised by evporation are and mires MAAE/MAF: USA Delaware, In-out GW/D WB Ponds inputs water of 90% about for accounted inflow groundwater GDS: Comp NW Territories, Canada Africa West FP Floodplain In-out LTH vegetation swamp of areas vast by flattened is peak the FPLM:

. .

et et al et al et al. et al. (1993) (1993) Bullock (1992a) Bullock (1992b) Grillot & Dussarrat (1992) Klepper (1992) (1992) Price Newfoundland, Bucher (1993) Eggelsmann (1993) al. et Gibson Gilvear (1993) John Phillips & Shedlock (1993) Shedlock (1993) (1993) al.

385 Andy Bullock and Mike Acreman FEV: + FEV: + FPLM: . FPLM: - FPLM: . MAF: - MAF: DPFV: - - MAF: + MAAE: + DPAE: AGR: X . FPLM: DPFV: . AGR: + AGR: FEV: + - FRR: + FPLM: . FPLM: - FPLM: DPFV: - + FPLM: + FVa: AGR: - = AGR: FEV: + FEV: + + DPAE: AGR: X

-1 yr 3 by discharging groundwater was the major storm runoff mechanism mechanism runoff storm major the was groundwater discharging by (p.37) DPFV:summer low were flows slightly higher Finland: FPML: a slightthere was increase in peaks DPFV: a slight there was increase in low flows (p.62-66) 3.5% by increased volume runoff total MAF: by water loses and flows river by recharged is wetland the DPAE: (p.38) season dry the through evapotranspiration flood attenuating in role important an play not did wetland the FPLM: peaks DPFV: the wetland did not significant make contributions to streamflow (p.185) conditions flow river low under recharge than the uplands (p.205) (p.205) uplands the than recharge likelyare togreater be than in uplands because the higher degree of (p.28) gradients gentler and saturation... because lowered of groundwater. Peat in the Huhtisuo catchment had different topography and special hydraulic characteristics which resulted were floods on drainage peat of effects The flows. peak in increase an in on the depends drainage of effect basin.The Svartan the in negligible (p.657-9) level groundwater (p.97) flooding season wet annual demonstrate demonstrate DPFV: baseflow because minimal in thereis summer virtually no drainage the from peat (or clay) surface of production widespread given runoff flood high very FPLM: flow FVa: steep slope and therefore variability greater flow (p.25-26) (p.29) areas surrounding 12 Mm about losing catchment Bokaa DPAE: the large depression and detention storage of both systems systems both of storage detention and depression large the DPAE: (p.328) losses evapotranspiration enhanced (p.224) low be may sediments mineral discharged. quickly was water and fen the flooded flows storm FEV: GW Chem FEV: saturatedpermanently overland saturated from created flow areas

LTH the that AGR: volume of water discharges throughthebasal peat intothe GW GW Drained Drained CCM differed runoff nor peaks neither FPLM/MAF: Sweden: In-out Comp In-out WB recharge to contributions substantial make not did wetland AGR: Finland: fens fens Finland: fen and GW/S Swamp Comp GW/S Swamp GW/S slough Prairie In-out WB groundwater for effective more likely are depressions prairie AGR: GW/S bog Sweden: bogs Domed GW/S Peat SW/S Toronto, Toronto, Canada Saskatchewan, Canada USA Permafrost SW/S Wetland Sweden Same GW/S LTH Sweden and Finland areas Peat wetland in flow overland of duration and magnitude the FEV/FRR: Drained Labrador, S.E. Canada CCM FPLM: Swedish rivers showed drainage decreased flows after peak USA Nigeria FP Floodplain Same WB the is key The recharge. aquifer in role vital a play wetlands the AGR: Illinois, USA USA Illinois, SW/S Constructed Same WB (p.340) outflow of component a as (0-6%) low very was seepage AGR: X AGR:

(1993) (1993) et al. et al. Waddington et al. Woo & Rowsell (1993) Woo & (1993) Winter Hey Iritz (1994) & Johansson (1994) Seuna & Price Maloney (1994) (1995) Burt UK Doss (1995) SW/S Maine, USA (1995) Khan Malaysia Peat GW/D (1995) Meigh Botswana FP Bog Multiple (1995) FP Owen LTH Wisconsin, Floodplain comparatively basins peat-covered Comp from curves duration Flow Floodplain Same & Thompson (1995) Hollis Same WB CCM from than less be will swamp the from recharged groundwater AGR: the from loss water of cause major a was wetland the MAF/MAAE: (1994) (1994)

386 The role of wetlands in the hydrological cycle AGR: = FTTP: + FPLM: - MAAE: + GDS: = AGR: = GDS: = WPGR: + DPGR: - GDS: = AGR: = GDS: = WPGR: = AGR: = FEV: - )” (p. 195) 195) (p. )” -1 s ace aquifer isace recharged the by vertical percolation of 3 floodwater (p.172) (p.172) floodwater days later than at the upstream gauge (p.283) (p.283) gauge upstream the at than later days FPLM: reduction mean The in peak discharge between the two gauges 283) (p. 20% about was evaporation by lost basis…water annual on an Pantanal the from outflow 258) (p. precipitation direct by balance roughly is with areas of higherwith of areas inflows locatedcloserto river the (p. 505). measurements surface water inundating water surface measurements the wetland had sufficient of part upper the and unit confining the through to flow head hydraulic the alluvial aquifer to the lower part of the alluvial from aquifer and away (intermediatethe Black Swamp recharge).The greater the distance from the river, the the less likely groundwater the from to will site the flow river andthe more likely it will flow to the lower part of the aquifer (p 338) streamflow season dry maintains which groundwater ranged from –0.030m3/day during the late winter to +0.043m3day several several +0.043m3day to winter late the during –0.030m3/day from ranged 914) (p summer the during times the from discharge Dakota water aquifer of year, contributes less than a recharge- the budget… water wetland the to percent a of tenths few discharge functionLunby of and Stewart wetland is in a state of dynamic equilibrium (p. 119) WPGR:deeppenetration occur during may repeated, relatively brief recharge to spring corresponding gradient hydraulic reversed of periods 118). (p. rainfall normal above of periods and groundwater predominantly a is Marsh the that suggesting year, the the area,(p. especially recharge lying, lower areas 229). wetter minimum 3500ha of callow land is flooded to an average depth of 1m, 1m, of depth average to an flooded is land callow of 3500ha minimum this represents a storage equivalent to Shannon one of day peak discharge 400m (around During AGR: a significant percentage the of monthly level water of discharge by primarily controlled are levels water floodplain GDS: FEV: The floodplainsa considerable “have flood controlcapacity; the if GW GW T CCM Lake the into flow groundwater that show Results WPGR/DPGR/GDS: Comp CCM the of most over upward are gradients hydraulic although AGR/GDS: CHEM throughout downward generally are marsh the in gradients vertical AGR: Comp GW GW GW T GW Comp Comp around lakes lakes around lakes around FP Floodplain In-out Comp Wetlands SW/D In-out Floodplain FP Wetlands SW/D FP Comp FP Callow Floodplain In/out LTH 8 4 to occurred wetland the of downstream peaks Hydrograph FTTP: SW/D Marshes Comp FP Floodplain Comp Floodplain FP FP FP Floodplain In-out WB site on the cm/day 0.2-0.8 from range rates inflow Groundwater GDS: North Dakota, Dakota, North USA Eastern Arkansas, USA Dakota, North USA Eastern Arkansas, USA Shannon, Ireland Brazil Pantanal, FP Plata, La Argentina Floodplain WB In-out the to equal; approximately is rivers inflowing of discharges MAAE: Amazonia, Amazonia, Brazil Southwestern Southwestern Wisconsin .

et . et al et al. et al (1997) (1997) Hollis (1996) (1996) Hollis Senegal andGerla Matheney (1996) FP Gonthier (1996) Floodplain Same Hunt WB Hodnett surf the AGR: Matheney and (1996) Gerla Walton (1996) Hooijer (1996) Hamilton al. Logan and Rudolph (1997) (1997) (1997) (1996) (1996)

387 Andy Bullock and Mike Acreman AGR: = MAAE: - - MAF: - FPLM: AGR: = - FPLM: - FPHM: FTTP: + DPFV: + GDS: = DPFV: - DPAE: + GDS: x AGR: x WPGR: = - MAF: MAAE: + GDS: = FPLM: - - FPLM: - FEV: FTTP: + upstream of upstream -1 s 3 downstream compared with 15 m -1 s 3 AGR: The vertical hydraulic gradient was downward was throughout gradient hydraulic the vertical The AGR: to groundwater of 480mm the loss of system of to a total year…leading net groundwater becomes groundwater of flux although 2mm only to the to thesurrounding transferred rest aquifer; is vegetated recharge the areas where it is evaporated is greater wheat upland in the with planted evapotranspiration MAAE: (p.than 300mm) versus 53). in the (380mm wetland upstream (0.953 m 1874). (p. flows peak summer and mean (p. wetland 166) the target from seepage FPHM: floodplain reduced 19% flood (p. by peak 212) 35 Forandby FTTP: events, floodplain lag increased 4 hourstwo (p.212). respectively day around ML 0.65 of wetland the from discharge periods…a baseline 139) (p. measured usually was period study detailed dry the groundwater GDS: During the relatively flow component comprised an estimated 97% of the surface flow leaving (p.the wetland 139) during to flow and notsustain perennial is winter that available storage term long as effective not raised bogs are very periods… dry rewetted storage areas and regulators of stream flow since low, zero or usually very were during yields DPAE:summer Water through lost and evaporation was rainfall the summer of most transpiration. bogs peat of raised feature not typical is groundwater a flow GDS/AGR: (p. 46). rainfall heavy dependant exceptionally of upon years 3mm is (with wetlands) in catchment therunoff Aroca MAF: Surface (without) (p. 67). catchment in Nyabesheki the tocompared 34mm been have subjected to show waters data thatIsotopic MAAE: river a have water waters…surface than wetland evaporation less significantly to exposure (p. leads to greater prolongedevaporation which residency, 66). on average to a stream where flow is about flow where toon 200 stream a average l/s. (p. 400). the wetland area). (p.53). area). the wetland attenuated of FEV/FTTP: in the terms flood greatly wave wetland the (p. 53). and timing volume GDS: aroundOn the Shingobee provide wetlands the river river, 46.3l/s GW WB LTH DPFV: producedis yield show data previous water The that during most Comp GW In-out WB grid boxes both in model reduced addition The MAF/FPLM: wetlands of Comp Pair LTH 1988-1993, Between WPGR: and in occurred was recharge oneonly year Pair Pair floodplain wetlands drainage channels FP Deltaic FP Deltaic GW/D Slough In-out CHEM/ CHEM/ Slough GW/D In-out General Canal GW/S Headwater In-Out WB GW/S was themonth canal each entering 50-90% between water of AGR: swamp Reed In-Out Bog SW/S WB Drained/ DPFV: over extended negligible was into although flow the wetland Aral Sea, Uzbekistan Saskatchewan, Saskatchewan, Canada Canada Alberta, FP Floodplain In/out Everglades, USA SEH Minnesota, flow 6% of the was FPHM:peak of the wetland Flow downstream USA Devon, England FP North-east Floodplain Victoria, Australia In-Out SEH Lower Saxony, Germany FPLM: floodplain reduced flood by 7% (p.212) peak Swamp-filled GW/S Uganda

et al. et al. et al. et al. (1999) Hayashi Hayashi (1998a and 1998b) Hillman (1998) Ferrari Genereux and Slater (1999) (1999)Gerla Central Hardy (2000) Raisin (1999) Spieksma (1999) and Taylor Howard (1999)

388 The role of wetlands in the hydrological cycle AGR: = GDS: = FEV: + AGR: + AGR: = for -1 (p. 452). 452). (p. -1 AGR/GDS: Estimated netAGR/GDS: groundwaterentirelyalmostfluxes were negative values indicating that ground-water recharge commonly water the of 31% discharge…approximately ground-water exceeded system. aquifer underlying the to recharge provides supplied 510) (p. (2.8%) comparison in negligible was discharge Groundwater generation” runoff storm of mechanism principal the is flow from the floodplain. A difference in flood level of 0.6m was was 0.6m of level flood in difference A floodplain. the from flow accompanied by a difference in groundwater storage, expressed 3m.” in termsleast at of level groundwater of two wetlands, but in wetland N, underlain by a thick layer of blue clay clay blue of layer thick a by underlain N, wetland in but wetlands, two onlythis yr one was cm lateral and infiltration by recharged is groundwater “…shallow AGR: GW WB Comp GW In/out CHEM, In/out WB yr 17cm was aquifer underlying the into seepage deep Annual AGR: channel wetlands SW/D Drainage Comp FP Swamp Everglades, USA Zimbabwe GW/S Dambo USA Florida, FP In/out Okavango, Botswana WB cypress Pond FEV:saturation“… overland flow, arising withinof the the dambo, area Choi and and Choi Harvey (2000) McCartney (2000) Riekirk and Korhnak (2000) Wolski (2002)

389