Determination and Implementation of Environmental Water Requirements for Estuaries

Ramsar Technical Reports

Ramsar Technical Report No. 9 CBD Technical Series No. 69

Determination and implementation of environmental water requirements for estuaries

Janine Adams 09

Ramsar Technical Report No. 9 CBD Technical Series No. 69

Determination and implementation of environmental water requirements for estuaries

Janine Adams

Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth, 6031, South Africa Email: [email protected] Fax: +27 41 5832317 Telephone: +27 41 5042429

Ramsar Convention Secretariat Secretariat of the Convention on Biological Diversity Rue Mauverney 28 413, Saint Jacques Street, suite 800 1196 Gland, Switzerland Montreal, Quebec, Canada H2Y 1N9

December 2012 Ramsar Technical Reports

Published jointly by the Secretariat of the Convention on Wetlands (Ramsar, Iran, 1971) and the Secretariat of the Convention on Biological Diversity. © Ramsar Convention Secretariat 2012; © Secretariat of the Convention on Biological Diversity 2012. This report should be cited as: Adams, Janine. 2012. Determination and implementation of environmental water requirements for estuaries. Ramsar Technical Report No. 9/CBD Technical Series No. 69. Ramsar Convention Secretariat, Gland, Switzerland & Secretariat of the Convention on Biological Diversity, Montreal, Canada. ISBN 92-9225-455-3 (print); 92-9225-456-1 (web). Series editors: Heather MacKay (Chair of Ramsar Scientific & Technical Review Panel), Max Finlayson (former Chair of Ramsar Scientific & Technical Review Panel), and Nick Davidson (Deputy Secretary General, Ramsar Convention Secretariat). Design & layout: Dwight Peck (Ramsar Convention Secretariat). Cover photo: Estuário do Sado Ramsar Site, Portugal (Nick Davidson) Ramsar Technical Reports are designed to publish, chiefly through electronic media, technical notes, reviews and reports on wetland ecology, conservation, wise use and management, as an information support service to Contracting Parties and the wider wetland community in support of implementation of the Ramsar Convention. In particular, the series includes the technical background reviews and reports prepared by the Convention’s Scientific and Technical Review Panel (STRP) at the request of Contracting Parties, which would previously have been made available in most instances only as “Information Papers” for a Conference of the Parties (COP), in order to ensure increased and longer-term accessibility of such documents. Other reports not originating from COP requests to the STRP, but which are considered by the STRP to provide information relevant to supporting implementation of the Convention, may be proposed for inclusion in the series. All Ramsar Technical Reports are peer-reviewed by the members and observers appointed to the STRP and independent experts. Ramsar Technical Reports are published in English in electronic (PDF) format. When resources permit, they are also published in French and Spanish, the other official languages of the Ramsar Convention. The views and designations expressed in this publication are those of its authors and do not represent an officially-adopted view of the Ramsar Convention or its Secretariat or of the Convention on Biological Diversity or its Secretariat. Reproduction of material from this publication for educational and other non-commercial purposes is author- ized without prior permission from the Ramsar and CBD Secretariats, providing full acknowledgement is given. For further information please contact:

Ramsar Convention Secretariat Secretariat of the Convention on Biological Diversity Rue Mauverney 28 413, Saint Jacques Street, suite 800 CH-1196 Gland Montreal, Quebec, Canada H2Y 1N9 Switzerland Tel: +1 (514) 288-2220 Fax: +41 (22) 999 0169 Fax: +1 (514) 288-6588 E-mail: [email protected] E-mail: [email protected] Web: www.ramsar.org Web: www.biodiv.org

ii Environmental water requirements for estuaries

Ramsar Technical Report No. 9 / CBD Technical Series No. 69 Determination and implementation of environmental water requirements for estuaries

Janine Adams

Contents Foreword iv Acknowledgements iv Summary 1 1. Introduction 1 1.1 Ramsar guidance and other materials related to this report 1 1.2 Terminology: “environmental flows” and “environmental water requirements” 2 1.3 Scope and purpose of this report 2 2. The importance of freshwater inflow to estuaries and the changes in estuaries in response to 4 altered freshwater inflow 2.1 Estuary types 4 2.2 The response of estuaries to changes in freshwater inflow 4 Influence of changes in freshwater inflow on estuary mouth closure 5 Influence of changes in freshwater inflow on salinity 5 Influence of changes in freshwater inflow on water quality 5 Influence of changes in freshwater inflow on fisheries 6 Sensitivity of different estuary types to changes in freshwater inflows 6 Summary 9 3. Methods and frameworks used to determine the environmental water requirements of 9 estuaries 3.1 Inflow-based methods 9 3.2 Resource-based methods 9 3.3 Condition-based methods 11 3.4 Holistic Ecosystem Methods and Frameworks 11 3.5 Models as tools in environmental water requirement studies 14 4. Trends in method development and implementation 16 4.1 Factors influencing method development and implementation 16 4.2 Freshwater requirements of the marine environment 16 4.3 Institutional barriers to implementation 17 4.4 Adaptive management of freshwater inflows to estuaries 17 4.5 Implications of climate change 18 5. Conclusion 18 Strengthening implementation 18 Improving data and knowledge 18 Transferability of methods and frameworks 18 Including social, economic and cultural issues 18 6. References 19 Annex 27

iii Ramsar Technical Reports

Foreword The importance of water management for the wise use of wetlands has been a key theme in the Resolutions and guidance adopted by the Ramsar Convention, as well as being highlighted in the original text of the Convention itself. Following the adoption of Resolution VI.23 (Ramsar and Water) in 1996, Ramsar’s suite of water-related guidance has been steadily expanded, and it has been brought together in the 4th edition of Ramsar Handbooks 8 (Framework for the Convention’s water-related guidance), 9 (River basin management), 10 (Water allocation and management), 11 (Managing groundwater), and 12 (Coastal management). The present report, which provides a review of methods for determination and implementation of environmental water requirements for estuarine wetland ecosystems, was prepared in response to a request from the Convention’s Contracting Parties to the Scientific and Technical Review Panel (STRP) which is reflected in Task 3.3 of the STRP Work Plan for 2003-2005 for the Panel’s expert working group on Water Resource Management. This report complements the adopted guidelines for the allocation and management of water for maintaining the ecological functions of wetlands (Resolution VIII.1, 2002), and focuses on a specific wetland type, namely estuaries. The ecological functioning of estuaries depends on inflows from both the adjacent coastal marine waters as well as freshwater inflows from the river basin upstream. The complex relationship between these two inputs determines, to a large extent, the nature of the estuarine ecosystem and associated services which are provided by that ecosystem. Understanding how the relationship between freshwater inflows and marine inflows can be affected by different drivers, including human activities, is essential to achieving the wise use of estuarine wetland ecosystems. Dr Heather MacKay, Chair of the Scientific and Technical Review Panel 2009-2012 December 2012 Acknowledgements Sharon Birkholz of the Institute for Water Research (Grahamstown, South Africa) and Rebecca Tharme of The Nature Conservancy are thanked for inputs to early drafts of this report, with the assistance of funding from the Water Research Commission of South Africa. The author also thanks John Sherwood (Deakin University, Victoria, Australia), Keith Bishop (NSW, Australia), Paul Montagna (University of Texas at Austin, USA), Susan Taljaard and Lara van Niekerk (CSIR, South Africa) and Julie Robins (Department of Primary Industries and Fisheries, Queensland, Australia) for their updated references and reports. Two independent reviewers provided helpful comments and recommendations to improve the report, and members of the Scientific and Technical Review Panel of the Ramsar Convention are thanked for their comments on earlier drafts.

Morston, the "North Norfolk Coast" Ramsar Site in the UK. Photo: Nick Davidson, Ramsar.

iv Environmental water requirements for estuaries

Summary This report provides a review of available methods for determining the environmental water requirements of estuaries, as well as a discussion of trends in method development and requirements for the successful implementation of environmental water requirements. In most countries the environmental water requirements of estuaries have only recently received attention – in the past these requirements were seldom considered in water resources planning and environmental management, mostly because of the lack of long-term monitoring data on estuarine ecosystems and a limited understanding of the influence of freshwater inflow on the structure and function of estuaries. In some cases it was incorrectly assumed that the environmental water requirements determined for rivers would protect downstream estuarine processes, and in other cases the omission was a result of divided sectoral management of water resources or lack of applicable legislation. Three countries have made substantial progress in developing methods for assessment of environmental water requirements for estuaries, i.e., Australia, South Africa and the USA, and the main focus of the report is on their experiences. Methods have mostly been developed within practical applications, representing a “learning-by-doing” approach. Recently-used methods take a holistic and adaptive approach and are presented as frameworks that include a number of steps and provide a broad strategy for assessment of environmental water requirements for estuaries. These frameworks also include elements of risk assessment and adaptive management. Most approaches ��are data-intensive and emphasize long-term monitoring so that the impacts of freshwater inflow alteration can be understood. Because of limited financial resources, some countries have prioritized specific estuaries for assessment. In other countries, legal battles relating to water use and allocation have resulted in the execution of detailed modeling and monitoring exercises, the development and testing of methods, and the implementation of water allocations to meet environmental water requirements. This review demonstrates that a range of methods and frameworks is available for determining the environmental water requirements of estuaries. Implementation is currently slow, however, because of costs and lack of expertise as well as inadequate institutional and legal arrangements. Technical expertise is required especially for modeling sediment, hydrodynamic and water quality processes in estuaries and linking these to biotic responses in order to understand the implications for determination of environmental water requirements. Successful implementation of environmental water requirements for estuaries has occurred where there have been strong governance structures, stakeholder participation, monitoring, and feedback in an adaptive management cycle.

1. Introduction (COP8) to review Resolutions VIII.1 and VIII.2 and to prepare further guidance for consideration at COP9. 1.1 Ramsar guidance and other materials The STRP’s 2003-2005 Work Plan for Working Group related to this report 4: Water Resource Management included the prepa- ration of ‘Guidance for environmental flow assess- In 2002, Contracting Parties to the Ramsar Convention ment for wetland ecosystems’ (Task 3.3) as one of its adopted two Resolutions relating to environmental priorities, with the following objectives: water allocations: i) To prepare reviews and associated guidance for • Resolution VIII.1 (Guidelines for the allocation and Contracting Parties for COP 9 on environmental management of water for maintaining the ecological flow methodologies for rivers and other types functions of wetlands); of wetland ecosystems and their biophysical • Resolution VIII.2 (The Report of the World components, appropriate for regulated systems Commission on Dams and its relevance to the Ramsar - with particular attention given to assistance in Convention). the management of dam-related impacts - and unregulated systems; In addition, the STRP was requested in 2002 at the 8th meeting of the Conference of Contracting Parties ii) To prepare guidance, as appropriate, on the processes of determining and implementing environ- 1 Ramsar Technical Reports

mental flows, building on the existing guidance 1.3 Scope and purpose of this report provided at COP8 (Resolutions VIII.1 and VIII.2, n the Ramsar Classification System for Wetland and supporting papers) and a synopsis of mate- Types, estuaries fall under Marine and Coastal rial derived from the technical reviews. I waters (Category F) where they are defined as includ- This Technical Report has been prepared in response ing the permanent waters of estuaries and estuarine to that request to STRP reflected in Task 3.3(i) in the systems of deltas (Ramsar Convention, 1996). They 2003-2005 Work Plan; it also serves as supplementary are distinct and valuable environments in which con- material related to the following Ramsar Handbooks tinual mixing of freshwater and marine water gener- (Ramsar Convention, 2011): ates a complex array of habitats. Estuaries perform important chemical and physical functions; they trap • Handbook 8 (An Integrated Framework for the nutrients, filter toxic pollutants and transform wastes Convention’s water-related guidance); that enter from the watersheds, nearshore ocean, • Handbook 9 (Integrating wetland conservation and and the atmosphere. Physical functions of estuaries wise use into river basin management); include the amelioration of coastal storm impacts, • Handbook 10 (Guidelines for the allocation and man- the attenuation of flooding, and the mitigation of ero- agement of water for maintaining the ecological func- sion on bordering landmasses (Davidson et al., 1991; tions of wetlands); and Kennish, 2000). Commercial activities related to estuaries frequently include shipping, marine transporta- • Handbook 12 (Wetland issues in Coastal Zone tion, oil and gas recovery, electric power generation, Management). marine biotechnology, aquaculture and mariculture, fisheries production and tourism. Other benefits 1.2 Terminology: “environmental and services often provided by estuaries include flows” and “environmental water sediment supply, soil formation, genetic resources, raw materials for subsistence and commercial use, requirements” aesthetic value, cultural and educational value and t present there is no single, internationally- water supply. Table 1 gives an overview of the eco- Aagreed definition of the term “environmental system services provided by estuaries. water requirements”, and the terminology continues Implementation of environmental water requirement to evolve over time as the concept becomes more determinations is recognised as being important to widely accepted and applied. The term “environ- support the intrinsic, ecological, social and economic mental flow (or flows)” has been most commonly values of estuaries. However, much research in the adopted to date, irrespective of whether the water field of environmental flows has focused on methods in the wetland is flowing or not, and this probably for rivers with much less attention given to -meth reflects the limited attention currently given to wet- ods for estuaries. There are a number of well-docu- land ecosystems other than rivers. In this report the mented and widely used methods such as In-Stream more general term “environmental water require- Incremental Methodology (IFIM), habitat analysis, ments” is used in respect of both flowing and non- and Building Block Methodology (BBM) (King and flowing systems, unless another term is used ina Louw, 1998). Recently, practitioners in the field have specific source document, example or case study. adopted a more holistic approach to assess the envi- “Environmental flows” (or, in this report, “environmental water requirements not only for the river ronmental water requirements”) refers to the water system but also the associated wetlands, groundwa- regime of a river, wetland or coastal zone necessary ter and estuary systems (Acreman, 2003). In most to maintain the biophysical components, ecologi- countries the environmental water requirements of cal processes, and health of aquatic ecosystems and estuaries have only recently received attention. In associated ecological goods and services (Arthington the past these requirements were ignored, largely et al., 2006). The concept of Environmental Flows because of the lack of long-term monitoring data and is rapidly developing into a suite of frameworks an understanding of the structure and function of and tools for the protection and restoration of estuaries. In some cases an incorrect assumption was inland and coastal aquatic ecosystems (Naiman et that the environmental water requirements deter- al., 2006). Environmental Flows is a sub-discipline mined for rivers would protect downstream estua- of Ecohydrology which encompasses all aspects rine processes, while in others the omission was the of research related to flow-ecology relationships result of the divided sectoral management of water (Hannah et al., 2004; Naiman et al., 2006). resources. 2 Environmental water requirements for estuaries

Table 1. Ecosystem services of aquatic and water-dependent ecosystems and their importance in estuaries (from Van Niekerk and Turpie, 2012, adapted from Costanza et al., 1997 and Turpie and Clark, 2007)

Ecosystem services Description Importance in estuaries Water Provision of water for subsistence and agricultural Low use (only applicable in fresher upper reaches) Food, medicines Production of fish and food plants; medicinal High plants

(goods) Raw materials Production of craftwork materials, construction Medium to materials, fodder and biofuel (especially important high

Provisioning services in rural and arid areas) Climate regulation Carbon sequestration, oxygen and ozone produc- High tion, urban heat amelioration Disturbance regulation Flood control, drought recovery, refuges from pol- High lution events Water regulation Provision of dry season flows for agricultural, Low industrial and household use (only applicable in fresher upper reaches) Erosion control and Prevention of soil loss by vegetation cover and High sediment retention capture of soil, e.g., reeds and sedges preventing Regulating services bank erosion Ecological regulation Regulation of diseases and pests such as malaria, High bilharzia, liver fluke, black fly, invasive plants due to the effects of salinity. Waste treatment High retention, therefore effective in breaking Medium to down waste and detoxifying pollution. Tidal and high fluvial flushing assist with dilution and transport of pollutants

Refugia/ Nursery areas Critical habitat for migratory fish and birds, High important habitats or nursery areas for species

Export of materials and Export of nutrients and sediments to marine High nutrients ecosystems Supporting services Genetic resources Medicine, products for materials science, genes for Low resistance to plant pathogens and crop pests, orna- mental species

Structure and com- The characteristics, including rarity and beauty, High position of biological that give an area its aesthetic qualities or make communities it attractive for recreational, religious or cultural services Cultural activities (attributes)

This review focuses on the methods and frameworks able methods, to describe recent trends in method developed for assessment of the environmental water development, and to identify requirements for the requirements of estuaries. The objectives of this study successful implementation of environmental water were to assess the strengths and weaknesses of avail- requirements for estuaries. 3 Ramsar Technical Reports

2. The importance of freshwater inflow River mouths are dominated by riverine influences to estuaries and the changes in and can take the form of a single or multiple-mouth estuary. The estuary is usually fresh or oligohaline estuaries in response to altered (salinity < 5 ppt) but conditions can range from river- freshwater inflow ine to estuarine. he importance of freshwater inflow to estuaries Valleys are located in a drowned river valley and and the changes in estuaries in response to altered T can consist of a single channel or a number of tribu- freshwater inflow are discussed briefly below. Other taries. A full salinity gradient from fresh to marine studies have addressed this topic in greater detail conditions is common but the estuary is seldom (Browder and Moore, 1981; Drinkwater and Frank, hypersaline. 1994; Whitfield and Wooldridge, 1994; Bate and Adams, 2000; Alber, 2002; Estevez, 2002; Gillsanders Lagoons and lakes are located on a coastal plain and Kingsford, 2002; Fohrer and Chicharo, 2012). where there is a strong supply of marine sediment This section provides an overview of the topic for the which results in the development of barrier beaches, benefit of readers new to the field. dunes or bars. These systems can become closed to the sea, resulting in hypersaline conditions. 2.1 Estuary types Changes in freshwater inflow will influence the mixing between fresh and saltwater, and this mixing classification of estuary types can provide a use- determines the physical and chemical properties of ful framework for understanding the character- A the estuary, the length of the estuary, inundation istics of estuaries in general, why they occur where levels, and residence time (Fohrer and Chicharo, they do, what features they share and, most impor- 2012). Mixing processes are influenced more by the tantly, how they function (Davidson et al. 1991). river inflows in estuaries of the river mouth type. However, this is a complex and difficult task because Tides and river inflows are important in valley of the high variability that exists among estuaries types, whereas wind can control mixing processes in worldwide. Classification has generally been aimed lagoons and lakes. at grouping estuaries based on different characteristics, including such aspects as geological (e.g., sub- strate type, historical formation and depth), physical 2.2 The response of estuaries to changes (e.g., circulation, currents and mouth states), chemi- in freshwater inflow cal (e.g., nutrients, pH, turbidity, salinity and dis- ny long-term change in the quantity, quality solved oxygen levels) and biological (e.g., commu- and timing of freshwater inflow will influence nity composition and food web structure) character- A the structure and function of an estuary through istics (Simenstad and Yanagi, 2012). changes in geomorphology, hydrology, water qual- Whitfield and Elliot (2011) classified estuaries into ity, exchanges with the sea, habitat availability, con- three primary categories (river mouths; valleys; lakes nectivity and ecological processes. Changes typically and lagoons) based on geomorphology (estuary mor- include a reduction of freshwater inflow volume, phometrics and mouth dimensions) and hydrogra- but human interventions can also lead to increases phy (river flow and salinity). This is a useful classi- in freshwater inflow through interbasin water trans- fication for determining sensitivity of an estuary to fers, agricultural return flow, and stormwater flows changes in freshwater inflow (Tables 2 and 3): from urban areas. These changes will alter the ability of the estuary to provide the goods and services that

Table 2. Primary estuary types and the relationship to other existing classifications (Whitfield and Elliot, 2012) Estuary ecosystem Alternative terminology used in classifications by others type River mouths Delta front estuaries and deltaic formations Valleys Drowned river valleys, fjords, fjards, firths, rias, estuarine bays, and some -tec tonic estuaries Coastal lakes and Blind estuaries, bar-built and intermittently open estuaries, coastal plain estuar- 4 lagoons ies, barrier beaches and estuarine embayments Environmental water requirements for estuaries

support mankind. Management of estuaries in terms reeds or even terrestrial species not resistant to salin- of the environmental water requirements is neces- ity. Closure of the mouth also prevents recruitment sary to balance the use of estuaries with the ability of invertebrates and fish to the estuary from the sea. to deliver goods and services. Tables 4 and 5 outline Freshwater inflow thus influences the ‘connectivity’ the responses of permanently open and intermit- of nursery habitats for certain species within estuar- tently closed estuaries to a reduction in freshwater ies. Species may inhabit a variety of freshwater and inflow which influences the abiotic characteristics, estuarine habitats at different stages of their life cycle causing changes in the abundance, productivity, dis- and the loss of connectivity between these habitats tribution, and composition of the biota. The effect of due to reduced freshwater supply can influence the these changes on the provision of ecosystem services survival of juvenile organisms reliant on those habi- is indicated. tats to complete their life cycle. To a large extent, the inflow of freshwater controls Influence of changes in freshwater inflow on the hydrodynamics of an estuary and therefore the salinity sediment transport within the system and the nature Reduction in freshwater inflow can result in saline of the mouth (i.e., whether open or closed). Upstream water extending further upstream and displacing dams can attenuate smaller river floods that might brackish habitats at the expense of saline habitats otherwise help to maintain the physical shape and (Adams et al., 1992; Wortmann et al., 1998). Freshwater structure of an estuary. Floods are needed to regu- inflow determines the extent of the longitudinal larly scour accumulated marine and catchment sedi- salinity gradient as well as the extent and structure ment from the estuary, deepening the mouth and of the vertical salinity stratification in an estuary. resetting the salinity regime. Upstream dams reduce Within this gradient, researchers have observed cer- the erosion capacity of river floods with the result tain areas, i.e., the river estuary interface (REI zone), that estuary channel dimensions shrink, sediments that appear to be biologically distinct and richer than accumulate in the subtidal zone, and flood tidal others (Bate et al., 2002). Reductions in freshwater deltas are deposited. Reduced freshwater input can inflow will shrink the most productive part ofthe thus result in sediment build-up and an increase in estuary; the brackish middle to upper or mesohaline the frequency and length of time during which the mixing zone of the estuary. Such compressions have mouth of an estuary is closed to the sea (see Table caused losses in primary and secondary productiv- 5). This will lead to reduced scouring of the bar at ity and fishery resources in certain Black Sea deltas the mouth and marked siltation of the channel (e.g., (Rozengurt and Haydock, 1981, cited in Jay and Tuggerah Lakes in New South Wales, Wilson Inlet in Simenstad, 1994). Western Australia; Lukatelich et al., 1987). Artificial breaching of the mouth may then become an option. Reduced freshwater inflow may result in the estu- In New South Wales, Australia, artificial breaching ary becoming hypersaline, particularly when this is is primarily undertaken to prevent flood damage to coupled with high evaporation rates and low rainfall. properties along estuary shorelines (Gillsanders and Alternatively, the opening of upstream impound- Kingsford, 2002). The situation is similar in South ment floodgates can also negatively affect the salinity Africa. regime in estuaries as a large release of freshwater can change the salinity in the estuary from full sea Influence of changes in freshwater inflow on water to full freshwater and back again over a short estuary mouth closure period of time (Irlandi et al., 1997). A sudden drop Freshwater input plays an important role in ensur- in salinity following a management response to high ing that the mouths of intermittently open estuaries salinity can result in severe physiological stress for remain open to allow tidal exchange with nearshore estuarine biota. marine water. Tidal exchange is important for the full Influence of changes in freshwater inflow on functioning of all estuarine attributes. For example, water quality any restriction of tidal exchange can lead to the loss of zonation and diversity of salt marsh plants which Freshwater inflow has a strong influence on the water are at the base of primary productivity. In high rain- quality characteristics of an estuary. The delivery of fall areas, if tidal exchange is restricted because of a dissolved and particulate matter and the concentra- closed estuary mouth, the water level in the estuary tions thereof is affected by changes in the timing and may rise and sediment salinity may be reduced for quantity of freshwater entering an estuary (Alber, long periods. This weakens salt marsh plants and 2002). Reduced input of nutrients and organic mat- allows encroachment into those areas by brackish ter to estuaries has implications for productivity and 5 Ramsar Technical Reports

trophic structure in these systems. Generally there is opening allowing water to “trickle” out to sea, but a positive relationship between phytoplankton bio- the mouth is then too perched and shallow for tidal mass and freshwater inflow, particularly as a result exchange. However seawater may enter the estuary of increased nutrient availability with increased during spring high tides (Van Niekerk et al., 2002). inflow (Malone et al., 1988; Mallin et al., 1993; Snow In principle all estuaries are sensitive to reduc- et al., 2000). The same pattern holds for pelagic con- tions and changes in freshwater inflow and studies sumers: both euryhaline copepods and fish attain sig- which determine the freshwater inflow requirements nificantly higher biomass in estuaries having a longi- should treat each estuary as a unique complex sys- tudinal salinity gradient (Schlacher and Wooldridge, tem. Indicators have been identified that could be 1996). Residence time (the length of time that material used to establish the extent to which estuaries would remains in an estuary) is also important, however. be sensitive to inflow modification (Taljaard et al., Influence of changes in freshwater inflow on 2004; Lamberth et al., 2008). The volume of the nat- fisheries ural mean annual runoff that an estuary receives is probably the most important parameter to consider Reduced fisheries production has been attributed when in judging the potential sensitivity to reduced to altered freshwater inflow in many estuaries, par- freshwater inflow. In general the larger the natural ticularly in those dominated by rivers (Livingston mean annual runoff into an estuary, the less sensitive et al., 1997). High spring run-off is a cue in the life it is likely to be to small reductions in river inflow histories of many fish and shellfish (Alber, 2002). as long as the mouth remains open most of the time. Whitfield (1994) found that the abundance of newly- However, the bathymetry of an estuary can cause recruited marine fishes into Eastern Cape estuaries, exceptions. In estuaries that are permanently open to South Africa, showed a significant positive correla- the sea the most important effect of reduced seasonal tion with longitudinal salinity gradients within the base flow or extended duration of low flow isan systems studied. It was suggested that it is the river- extension in the upstream intrusion of saline marine ine and estuarine olfactory cues associated with the water. Evaporation can result in hypersaline condi- salinity gradients which attract the postflexion larvae tions particularly in arid and semi-arid areas where and early juveniles into estuaries and not the salinity freshwater inputs are reduced in estuaries that are gradients per se. These findings were confirmed by closed to the sea (Table 3). James (2006) in laboratory experiments specifically designed to test those observations. The reasons that estuaries are often only intermittently connected to the sea include the size of the Sensitivity of different estuary types to estuary, the supply of marine sediment and the changes in freshwater inflows degree of wave action in and near the mouth, absence Bar-built or barrier estuaries are the types most sensi- of protection of the mouth by rocks, beach slope, and tive to change in freshwater inflow because a reduc- low mean annual run-off. Larger estuaries are less tion in freshwater inflow has the effect of increasing prone to mouth closure than are smaller estuaries the size of the bar at the estuary mouth, thus reducing because of greater tidal flow through the mouth – in the influence of the marine water inflows (Table 4). larger estuaries the tidal flow provides the primary Estuaries that normally only have intermittent con- driving force keeping the mouth open. Small estuar- nections to the sea are known as TOCEs (temporarily open/closed estuaries) in South Africa and ICOLLs Table 3. Sensitivity of different estuary types to (intermittently open lakes and lagoons) in Australia. changes in freshwater inflow These systems also occur on the southeastern coast of New Zealand, the southeastern coasts of Brazil and River Valleys Coastal Uruguay as a well as the southwestern coasts of India mouths lakes and Sri Lanka (Perissinottoet al., 2010). Many of these and systems have been degraded as a result of reduced lagoons freshwater inflow and eutrophication. Freshwater Mouth closure Low Moderate High abstraction can increase residence time of a body of & loss of marine water in an estuary, increasing pollutant concentra- connectivity tion and eutrophication. The three dominant hydrodynamic states in these estuaries are; open mouth, Eutrophication Low Moderate High semi-closed and closed mouth (Snow and Taljaard, Saline intrusion High Moderate Low 2007). In the semi-closed state, the mouth of an estu- 6 ary is nearly closed with only a shallow, narrow Hypersalinity Low Moderate High Environmental water requirements for estuaries

Table 4. Response of an open estuary to a reduction in water quantity (volume of freshwater inflow) and potential human impacts in terms of the provision of ecosystem services

Abiotic driver Biotic response Effect on ecosystem services SEDIMENT Increased marine Loss of open water habitat Activities such as boating & fish- sedimentation Biota with a preference for sand dis- ing affected place mud species Reduced input of fluvial Erosion and loss of wetland habitat Loss of ecotourism as areas with sediments recreational, tourist appeal lost No sediment input to Loss of habitat Loss of beaches, coastal erosion marine environment RETENTION Increase in stratification Death of sensitive organisms Bait collection & fisheries affected. and hypoxia of bottom Loss of protein rich food source waters Increase in retention of Accumulation of toxins in fish and Not suitable for consumption, pollutants shellfish reduced food supply Eutrophication and Toxic algal blooms Aesthetic appeal, recreation and decrease in water Decrease in biodiversity tourism lost transparency Loss of submerged aquatic vegetation Increased health risk form toxic algae blooms (ingesting blue green algae, shellfish poisoning) Reduced flushing of Accumulation of toxins in fish and Human health issues pathogens shellfish Aquaculture affected SALINITY Reduced freshwa- Loss of spawning and migration cues in Reduced fisheries ter inflow to marine the marine environment for invertebrate Loss of protein food source environment & fish recruitment

Longitudinal salinity gra- Decrease in habitat diversity Loss of estuary nursery function dient lost Reduced productivity in the river estu- - fisheries affected – loss of liveli- ary interface zone hoods for fishing communities Reduced fish & invertebrate recruitment Increase in saltwater Intrusion of marine predators, invasive Reduced fisheries intrusion alien species, parasites and diseases. Loss of brackish habitats, species rich- ness and productivity NUTRIENTS Reduced nutrient input Decrease in primary and secondary Loss of fisheries productivity

7 Ramsar Technical Reports

Table 5. Response of an intermittently closed estuary to a reduction in water quantity (volume of freshwater inflow) and an increase in the duration and frequency of closed mouth conditions. Potential human impacts in terms of the provision of ecosystem services are indicated.

Abiotic driver Biotic response Effect on ecosystem services No tidal exchange Loss of intertidal habitat and wetlands Wetland purification capacity, Loss of diversity (e.g., intertidal salt erosion control and flood mitiga- marsh & waders) tion lost Loss of marine Loss of invertebrate & fish recruitment, Reduced fisheries connectivity interruption of life cycles Decline in salt tolerant biota Loss of marine – catch- Loss of recruitment of catadromous spe- Reduced food security and loss ment connectivity cies that live in freshwater and breed in of cultural aspects the sea (e.g., eels & freshwater mullet) Increase in water level Loss of intertidal habitat e.g., intertidal Loss of tourist appeal, bird salt marsh and waders watching Surrounding property flooded which results in artificial breaching Decrease in water level Die-back of submerged plants Loss of bait and fisheries Nursery habitats for invertebrates and resources fish lost Reduced ecotourism Reduced foraging & nesting habitat for waterbirds. Eutrophication and Loss of submerged aquatic vegetation Loss of assimilative capacity decrease in water such as seagrass, harmful algal blooms, (waste treatment) transparency fish kills. Loss of fisheries Reduced recreational value Decreased value surrounding real estate Increase in retention of Accumulation of toxins in fish and Not suitable for consumption, pollutants shellfish reduced food supply Increase in retention of No contact recreational activi- human pathogens ties, declines in public health Hypersaline conditions Die-back of wetlands Banks destabilized, loss of buff- Change in species composition, reduced ers and flood control abundance and community composition.

ies have less tidal marine inflow and are very sensi- wave action, the greater the likelihood that the estu- tive to reductions in river inflow and thus reduction ary mouth will close. In estuaries where there is not in the amount of outflow, because this is the main a large amount of sediment available, for example force keeping the mouth open. If outflow decreases on a rocky coastline or where longshore transport is below a certain volume the mouth closes and remains quite far offshore, an estuary tends to be less likely to closed until such time as river inflow increases suffi- experience mouth closure due to river inflow reduc- ciently to cause the water level inside the estuary to tion. The mouth is also less prone to closure when rise and the mouth to be breached. it is protected against wave action, for example by a headland (Taljaard et al., 2004). The larger the amount of sediment available in the 8 adjacent marine environment, and the stronger the Environmental water requirements for estuaries

Summary resources is the basis of estuary environmental water requirement assessments and Alber (2002) classified In summary, changes in freshwater inflows, particu- the approaches into three types: larly those resulting from human activity, alter the dynamic nature of estuaries. This has serious impli- • Inflow-based methods determine an acceptable cations because the temporal and spatial hetero- level of deviation in freshwater inflows relative to geneity to which the biota have adapted is altered, the natural or reference freshwater inflow regime. sometimes permanently. Estuaries occur at the lower • Condition-based methods determine the fresh- ends of large river catchments but their complexity water inflow required to maintain agreed condi- and relatively small size makes them susceptible tions within the estuary. to human impacts upstream. The manner in which estuary characteristics are influenced by freshwater • Resource-based methods determine the freshwa- inflow is often not the result of a single flow event, ter inflow required to maintain suitable condi- but rather that of characteristic flow patterns occur- tions for particular resources (e.g., certain com- ring over weeks or months. In estuaries there is a mercially or culturally important species). much larger buffer or delay effect between river Table A.1 in the annex to this report indicates the inflow patterns and their effect on abiotic parameters countries and estuaries where these methods have than there is in rivers (Taljaard et al., 2004). For these been applied. reasons, methods for determining the environmental water requirements of rivers are not easily trans- ferred to estuaries. The strong longitudinal gradients 3.1 Inflow-based methods of abiotic characteristics and changes in response to nflow-based methods rely on hydrological analy- tides and freshwater inflow influence the biotic com- Ises and assume that if the inflow is maintained then position and function. Estuaries are complex systems this will maintain estuary condition and resources as which therefore require holistic and process-based well. The percent-of-flow approach (Flannery et al., approaches for determining the freshwater inflow 2002) is an inflow-based method for unimpounded requirements. A sound approach would require that rivers that was applied to Southwest Florida estuar- the investigator has an understanding of the natural ies. It set limits to freshwater withdrawals as a per- variability in the quantity and timing of freshwater, centage of stream flow at the time of withdrawal. including whether or not this has changed over time Other inflow-based methods such as the Indicators of and how it is likely to change in the future (Olsen Hydrologic Alteration (IHA) trend analysis method et al., 2006). Setting up scenarios of future possible have been applied to Georgia (USA) estuaries (Alber changes in inflow is important because they can be and Flory, 2002). effectively communicated to stakeholders as they identify the implications of alternative courses of The advantages of this approach are that it is simple, action in terms of the social, economic and ecological rapid and cost effective. However, the weaknesses are the lack of supporting ecological information implications. and the assumption that ecosystem change is linear and that only flow influences estuary health. The 3. Methods and frameworks used to approach would be less useful in highly-regulated determine the environmental water and altered systems. requirements of estuaries he term “Methods” describes the scientificscientifi c (tech-(tech- 3.2 Resource-based methods Tnical) tools used to investigate the freshwater esource-based methods focus on organisms inflow required to sustain the ecological function Rand fisheries that are of economic importance. of an estuary (Dyson et al., 2003). “Approaches” are Freshwater inflows are set on the basis of the require- ways of working to derive the assessments using, ments of the selected biotic or fisheries resources, and for example, expert teams, whereas “frameworks” the goal is to protect the estuary by focusing on key provide a broad strategy for assessments of envi- resources. One of the early studies considered the ronmental water requirements. Frameworks include pink shrimp, Farfantepenaeus duorarum, as an indi- a set of steps, linked components or tools that cover cator of the health and productivity of the Florida all aspects of the process of establishing agreed envi- Bay ecosystem. The pink shrimp simulation model ronmental flow allocations to estuaries (Gippel et al., (Browder et al., 1999) was used to show the influence 2009a). Understanding the relationships between of upstream water management and the response of freshwater inflow, estuary condition, and estuary the shrimps to changes in salinity. 9 Ramsar Technical Reports

Resource-based methods have also been used in rainfall variables. The method used to assess the Texas (USA), which has had a long history of envi- environmental water requirements of the Suwanee ronmental water management for estuaries. After River estuary involved the identification of ‘target a drought in the 1950s which caused low flow, habitats’ to be protected within the estuary (Figure hypersalinity, fish kills, and the loss of blue crabs 2). Thereafter, existing and new knowledge was used and white shrimp in the estuaries (Copeland, 1966; to recommend the salinities needed to sustain the tar- Hoese, 1967; Montagna et al., 2002), legislation was get habitats (Mattson, 2002). Five target habitats were passed to give consideration to the environmental identified and recommendations made in terms of water requirements of bays, estuaries and arms of the the freshwater inflow needs to maintain the salinity Gulf of Mexico. The Texas Estuarine Mathematical regime suitable to the particular habitat. Programming model (TxEMP, Matsumoto et al., 1994; The advantages of these resource-based methods Powell and Matsumoto, 1994; Powell et al,. 2002) was are that they have stakeholder buy-in because of the used to model salinity inflow and fishery harvest economic, social and political value of the resource, relationships. A series of relationships between his- particularly with regard to recreational and commer- toric monthly inflow and the catch of various fish, cial fishing. Therefore it is important that the indica- crustaceans and mollusks were used as the basis for tor chosen by the scientists should be linked to the the model (Matsumoto et al., 1994, cited in Alber, resources valued by society (Alber, 2002). These fac- 2002). Other resource-based methods have been used tors as well as the availability of time series data (from in the South Florida Water Management District and commercial catch or landing records) has resulted in in tropical Australia (Table A.1 in the annex to this environmental water allocations to sustain fisheries report). Halliday et al. (2003) and Robins et al. (2005) becoming a key feature of many Australian water developed a framework for determining environ- management plans (Halliday et al., 2003). mental flows to sustain estuary-dependent fisheries (Figure 1). Lack of data particularly with regard to commercial fisheries would limit the application of this- frame Robins et al. (2005) used correlative analyses in the work to other estuaries, and an obvious disadvan- Fitzroy River Estuary to relate catch to flow and

Figure 1. Generalised framework to identifying aspects of the freshwater flow regime that are potentially 10 important to estuarine fisheries production (after Robins et al. 2005). Environmental water requirements for estuaries

Figure 2. An example of the resource-based approach to assess the environmental water requirements of the Suwannee River Estuary, Florida (after Mattson, 2002). tage is that these methods are based on a limited salmon smolts and the abundance of planktivorous, number of species and their habitat requirements, piscivorous and bottom-foraging fish (Kimmerer and which may overlook other important resources with Schubel, 1994; Jassby et al., 1995). This X2 location different inflow requirements (Alber, 2002). Another changes in relation to the freshwater inflow into the disadvantage is that the models require large data estuary. sets even when the number of target species is small. An advantage of this approach is that it has many components of adaptive ecosystem management 3.3 Condition-based methods involving scientists, managers and a consortium of n this approach, environmental water require- federal and state agencies working in the estuary. Iments are set to maintain specific physical and The approach also considers all trophic levels (Alber, habitat conditions in order to protect the estuarine 2002). ecosystem. For example, the X2 approach sets the Disadvantages are that the approach excludes freshwater inflow to maintain specific conditions alternative models that could be explicitly tested (e.g., salinity) at a given point in an estuary. In the (Kimmerer, 2002) and the method can only be applied San Francisco Bay Estuary, California, freshwater in an estuary if empirical relationships between salin- inflow is managed so that the X2 (the distance from ity and ecological processes, e.g., phytoplankton pro- the Golden Gate Bridge to the 2 ppt isohaline, mea- duction, are understood. sured 1 m off the bottom and averaged over more than 1 day) is positioned where it may be beneficial 3.4 Holistic Ecosystem Methods and to aquatic life (CALFED, 2002, cited in Alber, 2002). Significant statistical relationships had previously Frameworks been found between X2 and the supply of phyto- he review of available methods indicates that plankton and phytoplankton-derived detritus, the Trecent studies have taken a holistic and adaptive abundance of mysids and shrimp, the survival of approach and are mostly presented as frameworks 11 Ramsar Technical Reports

which provide a broad strategy for the assessments mental water requirement assessment of the Jiaojian of environmental water requirements for estuaries. Basin, China, where researchers required a method Methods used in these frameworks are holistic, in which represented an asset-based, holistic approach that they consider the entire ecosystem and include (Gippel et al., 2009b). multi-disciplinary teams and stakeholders. Benchmarking is a “top down” method that defines Holistic ��methods have mostly developed from prac- environmental water requirements in terms of accept- tical applications, a learning-by-doing approach. For able levels of change from the natural flow regime example, in Australia Peirson et al. (2001) addressed (Arthington et al., 1998). The effects of changes are the requirements of the Richmond River estuary benchmarked by comparison with similar river which formed the basis of the proposed methods of reaches that have already been modified. The method the National River Health Program (Peirson et al., can be used to evaluate the consequences of many 2002). In South Africa scientists had been working different scenarios of flow regulation and appears to with the Department of Water Affairs and Forestry be suitable for poorly studied areas (Schofield et al., on the freshwater requirements of estuaries at least 2003). The concept of “benchmarking” has recently ten years prior to the formalisation of methods been incorporated into an environmental water in 1999 (Taljaard et al., 2004). Indeed a survey by requirement method called ELOHA (Ecological Moore (2004) and a question on how the concept of Limits of Hydrological Alteration). This approach environmental flows became established in various involves quantification of stress/response relation- countries elicited a majority response from respond- ships and environmental water requirement guide- ents that this was as a result of the introduction of lines for different classes of rivers with contrasting Environmental Flow Assessment (EFA) projects flow regime types (Arthington et al., 2006). It is a either by government agencies or sources from out- flexible framework for assessing and managing envi- side the country. ronmental water requirements across large regions and is being used to integrate environmental water Ecosystem-based approaches are more holistic, requirements into regional water resource planning but data requirements are intensive. An ecosystem- and management worldwide (Poffet al., 2010). based approach generally makes use of experts from a range of disciplines, with knowledge of both living Disadvantages of the benchmarking approach are (biotic) and non-living (abiotic) components of the that there are often uncertainties about processes at estuarine ecosystem, which implies that consensus the benchmark or reference estuary sites, and there among experts may not always be achieved (Dyson are difficulties in separating flow and non-flow et al., 2003). Studies vary in their selection of param- related impacts and understanding the lag effects of eters that are evaluated and the timeline over which impacts. The South African method for the determina- the implications of change are assessed. These types tion of the ecological reserve for estuaries (Resource of studies are generally replicable and can transfer to Directed Measures (RDM) method) addresses this by other sites or systems (Dyson et al., 2003). defining a reference state for each studied estuary. An Estuarine Health Index is then used to assess the Good physical, chemical, water quality and eco- present state of the estuary and deviation from the logical data are needed to determine appropriate reference condition (Figure 3). The health index iden- environmental water requirements. For example, tifies flow and non-flow related impacts. Theeco- fundamental to the FLOWS method used for estu- logical importance of an estuary (Turpie et al., 2002) aries in Victoria, Australia, is the development of together with the present state assessment is then flow relationships between physical and ecological used to recommend an Ecological Reserve Category objectives using conceptual models of key species which defines the level of protection afforded to an and processes. Conceptual models are also used in estuary. Resource Quality Objectives are also set to the benchmarking method in Queensland, Australia maintain water quantity, quality, habitat and biotic (Table A.2 in the annex to this report). The confidence integrity to keep the estuary in the recommended in the assessment is dependent on an understanding ecological state, and monitoring requirements are of the relationship between flows, abiotic and biotic identified. The method also evaluates different fresh- responses. Data are however not always available. water inflow scenarios. Hydrological specialists This was identified as a major stumbling block by the provide monthly runoff datasets for each scenario; different Australian states when the applicability of these are analysed by the hydrodynamic special- the Peirson et al. (2002) environmental water require- ists and then presented to ecological specialists for ment method was investigated (Gippel, 2002). The their assessment. This is an ecosystem approach that FLOWS method was also adapted in the environ- 12 requires an understanding of the effect of changes in Environmental water requirements for estuaries

Figure 3. The procedures for the determination of the preliminary ecological water requirements (reserve) for South African estuaries (after DWAF 2004). river inflow on abiotic components (e.g., hydrody- system approach that included aspects of risk assess- namics, sediment dynamics, and water quality) and, ment (Figure 4). In the absence of detailed hydrody- subsequently, the response of biotic components namic data on the Fitzroy River estuary, Australia, (e.g., microalgae, macrophytes, invertebrates, fish Gippel et al. (2008) applied a risk assessment and birds) (Adams et al., 2002; Taljaard et al., 2004; approach. Close (2005, 2007) reviewed reviewed DWAF, 2004). available methods for determining environmental water requirements for estuaries and recommended The South African method was developed in response the BAFFLER (Bayesian Adaptive Framework for to the National Water Act (No. 36 of 1998), which Flows to Maintain Estuarine Resources) approach to establishes the Reserve (of water) for basic human be followed for the Hill and Moore Rivers, Western needs and ecosystems, wherein a certain amount of Australia (Table A.2). This method relies on risk water must be set aside for basic human needs and assessment and incorporates levels of uncertainty ecosystems before water can be allocated for other and prediction of estuarine response to altered fresh- uses. Methods for the determination of the environ- water inputs. The approach includes monitoring and mental water requirements of estuaries were pub- adaptive management which allows for updating lished in 1999, and studies have been completed on a and re-evaluation of understanding and hypotheses variety of estuary types from different biogeographic and therefore improves decision making in knowl- zones in South Africa (see Table A.2 in the annex to edge-poor environments. A national framework for this report). According to Close (2005), a disadvan- assessing and implementing environmental water tage of the approach is that the risk to components requirements for estuaries in Australia has recently influenced by the flow alterations is not considered. been proposed (Gippel et al. 2009b). This is a two- Risk assessment approaches have been used in tiered approach, one for assessing simple, data-poor, Australia and the UK (Table A.2 in the annex to this low-value systems, or for prioritising multiple estu- report). The Peirson et al. (2002) method was an eco- aries, and a detailed approach for complex, data-rich, 13 Ramsar Technical Reports

Figure 4. The key steps used in the risk assessment/ecosystems approach used for Australian estuaries (after Peirson et al., 2002).

high-value estuaries. The detailed assessment is a Mexico, and in Samana Bay, Dominican Republic 13-step process termed an Estuary Flows Map. An (Table A.2). This is a low-cost approach suitable for use important aspect of this framework is the flexibility in developing countries that includes socio-economic to allow application of a range of scientific assess- aspects in the assessment. The framework involves ment methods to each particular estuary. stakeholders and incorporates both scientific and tra- ditional knowledge. The main goal is to create and Most of the recent approaches / frameworks have sustain a governance process that is just, transpar- identified the importance of adaptive management ent and accountable to those affected by its actions. and monitoring. Richter et al. (2005) proposed the The interests of the many upstream and downstream six-step ESWM (ecologically sustainable water man- stakeholder groups in the watershed and estuary are agement) framework which focuses on determining linked. This process involves the negotiation of plans the flow requirements of rivers prior to the com- and policies, subsequent decision making, monitor- mencement of hydropower projects and includes ing, education and enforcement. whole, functioning ecosystems (including estuaries), variable flow regimes, and use of interdisciplinary science teams. The case study was the Apalachicola 3.5 Models as tools in environmental water River and Bay where a flow regime was identified to requirement studies maintain the biological diversity and productivity of onfidence in the determination of the environ- the system (Richter et al., 2003). Implementation of mental water requirements of estuaries requires the flow recommendations occurs on a trial basis, the C detailed modeling studies linking hydrology, hydro- system is monitored to test responses and hypoth- dynamics, water quality, and biotic responses. eses, and further research is conducted if needed. Comprehensive environmental water requirement This framework was applied to the Savannah River- assessments for estuaries will always require some floodplain-estuarine system and used in the adaptive level of modeling, indicating the need for technical management of Thurmond Dam (Table A.2). expertise in these studies. Olsen et al., (2006) described the Integrated Water Early studies on the environmental water require- Resource Management (IWRM) framework which ments of estuaries were effective at modeling salinity was tested in the Laguna de Terminos Estuary, 14 changes and the effect on indicator organisms (e.g., Environmental water requirements for estuaries

Lambert and Fruh, 1978). Examples where simple Models have also attattempted empted to to integrate integrate the the physi physi-- models have been used to relate salinity structure cal, chemical and biological processes in an estuary. to freshwater flow include the investigations by Slinger (2000) identified and linked five models used Jassby et al. (1995) in California and an investigation to assess the environmental water requirements of for the Swan River, Western Australia, by Kurup et South African estuaries. These models were used al. (1998) (Table A.3 in the annex to this report). In to simulate the response of two estuaries to a range Tasmania, Davies and Kalish (1994) examined effects of inflow scenarios. In a study on three estuaries in of upstream storages on the flushing of the Derwent China, researchers incorporated three types of water Estuary, and Davies et al. (2002) investigated specific requirements into flow requirement calculations: flow requirements for the upper Derwent Estuary the water cycle, the biological cycle, and the habitat by modeling relationships between flow and ecosys- (Yang et al., 2005). A bioenergetic model was used by tem functioning. The U.S. Environmental Protection Hae-Cheol and Montagna (2009) to relate macroben- Agency (USEPA) Water Quality Analysis Simulation thic biomass and salinity regimes in order to assess Program (WASP5), which consists of two stand-alone the implications of changes in freshwater inflow to computer programs, was used to determine the fresh- benthic ecosystem dynamics. Ecohydrology mod- water allocations for the Pascogoula River and estu- els have now been applied to a number of estuaries ary (Harza 1995, cited in Peirson et al., 2002). Chan (Wolanski, 2007). Such a model was developed for et al. (2002) investigated the impacts of hydrological the low flow condition in the Guadiana Estuary in changes on the Swan River estuary using a coupled Spain and Portugal and was used to predict ecosys- hydrodynamic-ecological numerical model, which tem health and test the response of the system to dif- was employed to make assessments of pre-modifica- ferent management scenarios (Wolanski et al., 2006). tion and post-modification scenarios, with the major A combination of hydraulic and hydrodynamic mod- focus placed on the likely changes to phytoplankton eling and Geographic Information Systems (GIS) biomass and species composition. tools can be effectively used to communicate about

Figure 5. A decision tree used to determine the type of numerical model most suited to estuaries (1D = one dimensional, 2D = two dimensional, 2Dh = two dimensional horizontal, 3D = three dimensional (after Van 15 Ballegooyen et al., 2004). Ramsar Technical Reports

environmental water requirements, as was done for ing environmental water requirements for approxi- the delta of the Senegal River (Duvail and Hamerlynk, mately 5% of the country’s estuaries. 2003). The delta was substantially modified by the Other countries where initiatives are underway are construction of the Diama dam in 1986, after which China (Sun and Yang, 2004; Sun et al., 2008; Sun et al., no floods reached the floodplain or estuarine areas 2009; Zhao et al. 2009), Taiwan (Liu et al., 2005), the downstream, which remained dry. In 1994, managed Dominican Republic and Mexico (Olsen et al., 2006). flood releases from the dam were initiated. Hydraulic Tasmania is in the process of developing and refining modeling was developed as a tool to support stake- an environmental water assessment methodology holder negotiations on the desired characteristics through the Tasmanian Environmental Flows Project of the managed flood releases. Initially, a water (TEFlows Project) (Gippel et al., 2009a). balance model was developed. The data were then integrated into a one-dimensional hydraulic model, Different methods are developed and used in MIKE 11 (DHI, 2000). When associated with a Digital response to different social, economic and political Elevation Model and a Geographic Information pressures. In China the influences of changes in run- System (ArcView), the model provided a dynamic off in the Yangtze Estuary were studied before the description of floods. Flood extent, water depth, and construction of the Three Gorges Dam (Luo and Shen, flood duration data were combined with ecological 2002; Chen and Chen, 2002, as cited in Sun and Yang, and socio-economic data. The water requirements of 2004). The USA has the longest history of environ- the different stakeholders were converted to flood mental water assessments for estuaries, which have scenarios and the benefits and constraints analysed. often been prompted by drought and deterioration A consensus scenario was reached through a partici- in estuarine health. In Europe the focus is more on patory process (Duvail and Hamerlynck, 2003). estuary water quality: management objectives are set for estuaries through the Water Framework Directive The purpose of the study, complexity of the estuary, to achieve good ecological status in all water bodies and available expertise will determine the type of (Acreman et al., 2010). model to be used. For example, there are a number of predictive tools that can be used to assess the Dam construction and the necessary environmental hydrodynamics (or water circulation patterns) of impact assessments have resulted in a number of estuaries. These range from 3D numerical models, studies. In Portugal, Morais et al. (2009) investigated 2D numerical models, 1D numerical models, water the changes in the Guadiana Estuary in response to balance models, and statistical relationships to con- the filling of the Alqueva Dam. ceptual models (Van Ballegooyen et al., 2004). Figure 5 indicates a decision tree for application of numeri- 4.2 Freshwater requirements of the marine cal modeling. Numerical modeling can be used to environment assess the incremental effects of changes in river inflow which are difficult to derive from a number of stuarine habitats often extend beyond the mouth once-off sampling surveys. Eof an estuary, and offshore habitats in the marine environment are dependent on nutrient and sediment inputs from catchments (Loneragan and Bunn, 4. Trends in method development and 1999; Robins et al., 2005; Lamberth et al., 2009). In implementation any environmental water requirement study this is an important aspect that needs to be identified at the 4.1 Factors influencing method onset. In this context, Tasmania now requires that development and implementation freshwater allocations be determined for freshwater dependent ecosystems (Pinto, in Gippel, 2002). The lthough there has been an increase in the devel- omission of methods for determination of environ- opment and application of environmental A mental water requirements of the marine environ- water requirement assessment methods for estuar- ment from the current South African methods comes ies, this review has found that substantial progress as a result of the divided sectoral management of in implementation has primarily taken place in three water resources and marine resources (Taljaard et al., countries: Australia, South Africa, and the USA. 2004). Worldwide there is a need for integrated water South Africa has assessed the environmental water resource management and a catchment to coast eco- requirements of approximately 10% of the country’s system management approach. The term Integrated estuaries using the same method each time, whereas Coastal and River Basin Management is being used Australia has applied different methods to determin- 16 by UNEP (http://www.gpa.unep.org) (Olsen et al., Environmental water requirements for estuaries

2006), which reflects growing recognition of this science as knowledge progresses which would facili- need. tate optimal management and use of environmental flows. 4.3 Institutional barriers to implementation Monitoring has been occurring since 1997 in the major stumbling block to the assessment lower Hastings River, Australia, to detect impacts Aand implementation of environmental water caused by increased water extraction at Koree Island requirements is the lack of legislation and inad- (Bishop, 2005). Detailed studies in Australia include equate institutional and governance arrangements. those for the Murray River (South Australia, MDBC, Management of estuaries in most countries is shared 2000; Geddes, 2005; MDBC, 2008), Fitzroy Estuary among multiple government departments and coop- (Queensland), Derwent Estuary (Tasmania), and the erative governance is poor. For example in New Richmond Estuary (New South Wales). South Wales, Australia, water planning is adminis- The USA Texas Parks and Wildlife Department, tered by the Department of Water and Energy, while Coastal Fisheries Division, has an extensive moni- estuary management is driven by local government toring program for fish in all Texas bays, and the committees (Gippelet al., 2009a). The Murray-Darling Texas Water Development Board monitors and col- Basin receives water inflows from multiple states, lates river inflow and bay hydrographic data to esti- and therefore to ensure integration the Australian mate flows to the coast (Powellet al., 2002). Adaptive Commonwealth Government is responsible for management in allocating environmental water water planning across the whole basin. In Tasmania, requirements to the Nueces Estuary, Texas, has been estuarine water requirements were ignored because ongoing since the construction of the Choke Canyon it was assumed that the minimum flows determined Reservoir in 1982. This has been a stakeholder driven for rivers would protect downstream estuarine proc- process that has increased estuary health while esses. However, there is now growing recognition providing a sustainable water supply to the region that estuaries need separate environmental water (Montagna et al., 2009). requirement assessments (Gippel, 2002). In the Great Brak Estuary (South Africa), a mouth Moore’s (2004) survey on perceptions and interpreta- management plan involving water releases from the tions of environmental water requirements indicated Wolwedans Dam has ensured that the mouth has that the issue of implementation is a cause for con- remained open at important times, i.e., spring / sum- cern. Factors hampering implementation have been mer to ensure fish recruitment and survival of salt related to cost, expertise, adequate institutional and marsh (Adams et al.,1999). The construction of the legal arrangements, and effective stakeholder partici- dam 3 kilometers upstream of the head of the tidal pation. High confidence assessments require detailed influence of the estuary in 1989 reduced freshwater studies with high resource requirements and long input to the estuary and increased the frequency and time frames. Technical expertise is required to model duration of mouth closure (Slinger, 2000). the sediment, hydrodynamic and water quality proc- In the Savannah River system, water releases for esses. However, there are many occasions where ecosystem purposes have been conducted from lack of resources and data result in estuary water Thurmond Dam annually in spring since 2004 (Wrona requirement assessments based on expert panels and et al., 2007). As part of an adaptive management plan, qualitative risk assessments. Gippel et al. (2009a) sug- scientists have been monitoring the impact of flow gested bridging funding from national government restoration on various ecological processes and water to ensure implementation of estuary environmental quality. The process is iterative, where each control- water requirements until a “user pays” system could led flood pulse is viewed as an experiment that is be developed. monitored and scientifically refined over time. The resultant learning through testing, evaluation, and 4.4 Adaptive management of freshwater modifying management actions results in effective inflows to estuaries adaptive management (Holling, 1978; Walters, 1986). Central to the practice of adaptive management is here are a few successful case studies of adap- sustained and carefully targeted monitoring (Olsen tive management and monitoring in a number T et al., 2006). of countries. For nearly 20 years the adaptive management framework has been recognised as the most effective approach to natural resource management (Holling, 1978). This provides for the integration of 17 Ramsar Technical Reports

4.5 Implications of climate change Improving data and knowledge uture management of environmental water The implementation of environmental water require- Frequirements for estuaries will need to consider ments requires a sound understanding of estuarine climate change effects as changes in precipitation processes and the relationship between abiotic driv- and run-off will alter estuary responses. Sea level ers and biotic responses. Basic hydrological and rise, increased temperatures, and coastal storms will biological data are needed to improve confidence lead to changes in physical processes (e.g., modifica- in assessments. Quantitative data are required to tion in mouth conditions, salinity regimes, nutrient improve predictions so that there is less reliance on pulses, sediment regimes) and biological responses expert opinion. Research should focus on the identi- with an impact ultimately on ecosystem services. For fication and separation of flow and non-flow related example sea level rise and reduced freshwater inflow impacts. Information on ecological needs and toler- will increase salinity and result in longer flooding, ances of different biota are also important research leading to loss of salt marsh and mangrove habitat. topics. More demonstration flow restoration projects Banks will become destabilized, resulting in erosion are needed to validate conceptual models through and loss of buffers for flood control. According to action research. global climate change predictions, freshwater runoff Transferability of methods and frameworks to coastal areas will decrease in mid-latitudes and increase around the equator and at higher latitudes There are many ways in which estuaries have been (Day et al., 2012). The outer tropics and subtemper- defined, but this review has identified that the meth- ate zone will be drier, and high latitudes will become ods used to determine estuarine environmental water wetter. Management should focus on maintaining requirements have been influenced more by the healthy estuarine ecosystems so that they will be bet- available knowledge of the system in question and ter able to adapt to climate change. This may require the available budget than by the type of estuary. The ongoing review of and adjustments to the environ- same methods and frameworks are being applied mental water allocations for estuaries. across a variety of estuary types in both South Africa and Australia. 5. Conclusions Most of the recent methods for determining the envi- Strengthening implementation ronmental water requirements of estuaries fall into the holistic or ecosystem approach. Frameworks This review has shown that a range of methods have been developed which are not prescriptive is available for determining the environmental about which scientific methods should be used for water requirements of estuaries. What is urgently assessments. These frameworks include elements needed is the implementation of recommendations of risk assessment and adaptive management. Most to ensure the protection of estuaries and rehabilita- approaches are data rich and emphasize the need for tion of stressed or degraded estuarine ecosystems. long term monitoring in estuaries so that the impacts A method or framework will only be as good as the of freshwater inflow alteration and the variable protection the environmental water requirements nature of these systems can be understood. have afforded to an estuary. There will be progress Including social, economic and cultural issues if a learning-by-doing approach is initiated and there is implementation, monitoring, and feedback Because of the demand for freshwater resources in an adaptive management cycle. On the basis of and climate change effects on water availability, a number of international reviews, case studies and the necessity of environmental water requirement analysis, Le Quesne et al. (2010) proposed a number assessments for estuaries will increase. Future stud- of guidelines for advancing the implementation of ies should include social, economic and cultural environmental water requirements. 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The Morecambe Bay Ramsar Site in the United Kingdom. Photo: Nick Davidson, Ramsar 25 Ramsar Technical Reports

VAN NIEKERK L, TURPIE JK. (eds) 2012. South WOLANSKI E, CHICHARO L, CHICHARO MA, African National Biodiversity Assessment MORAIS P (2006) An ecohydrology model of the 2011: Technical Report. Volume 3: Estuary Guadiana Estuary (South Portugal). Estuarine Component. CSIR Report Number CSIR/NRE/ Coastal and Shelf Science 70, 132-143. ECOS/ER/2011/0045/B. Council for Scientific and WORTMANN J, HEARNE, JW and ADAMS JB Industrial Research, Stellenbosch (1998) Evaluating the effects of freshwater inflow WALTERS C (1986) Adaptive Management of on the distribution of macrophytes. Ecological Renewable Resources. Blackburn Press, New Modelling 106, 213-232. Jersey. WRONA A, WEAR, D, WARD J, SHARITZ R, WHITFIELD AK (1994) Abundance of larval and ROSENZWEIG J, RICHARDSON JP, PETERSON 0+ juvenile marine fishes in the lower reaches of D, LEACH S, LEE L, JACKSON R, GORDON J, three southern African estuaries with differing FREEMAN M, FLITE O, EIDSON G, DAVIS M freshwater inputs. Marine Ecology Progress Series and BATZER D (2007) Restoring ecological flows 105, 257–267. to the lower Savannah River: A collaborative WHITFIELD AK, WOOLDRIDGE TH (1994) scientific approach to adaptive management. : Changes in freshwater supplies to southern Proceedings of the 2007 Georgia Water Resources African estuaries: Some theoretical and practi- Conference, held March 27–29, 2007, at the cal considerations, p. 41–50. In K. R. Dyer and University of Georgia. R. J. Orth (eds.). Changes in Fluxes in Estuaries: YANG ZF, SUN T, QIN XS (2005) Calculating Implications from Science to Management. Olsen Methods for Quantifying Environmental Flows & Olsen, Fredensborg, Denmark. in Estuaries: A Case Study of Haihe River Basin, WHITFIELD AK, M ELLIOT (2011) Chapter 1.07 China. Journal Of Environmental Informatics 6 Ecosystem and biotic classification of estuaries (2), 72-79.. and coasts. In: McLusky, D. & Wolanski, E (ed.), ZHAO R, YANG ZF, SUN T, CHEN B and CHEN Treatise on Estuarine and Coastal Science, Volume GQ (2009) Freshwater inflow requirements for 12: Ecological economics of estuaries and coasts. the protection of the critical habitat and drink- Elsevier, Oxford. ing water sources in the Yangtze River Estuary, WOLANSKI E (2007) Estuarine Ecohydrology. China. Communications in Nonlinear Science and Elsevier, The Netherlands. 168 pp. Numerical Simulation 14, 2507-2518.

Fawley, the ‘Solent and Southampton Water’ Ramsar Site in the UK. 26 Photo: Nick Davidson, Ramsar. Environmental water requirements for estuaries

Annex Table A.1. Examples of inflow, condition and resource based methods used to determine the environmental water requirements of estuaries

Country Method Estuary Reference Inflow-based methods USA Percent-of-flow South-Western Florida estuaries Flannery et al., 2002 USA Water withdrawal Georgia estuaries: Savannah; Ogechee; Alber & Flory, 2002 regulations Altamaha; Satilla; St Marys Condition-based methods USA X2 approach San Francisco Bay estuaries Jassby et al., 1995 isohaline position Resource-based methods USA Pink shrimp model- Florida Bay, Florida, USA Browder & Moore, 1981, indicator species Browder et al., 2002 USA TxEMP Nueces Estuary, Galveston Bay & Matsumoto et al., 1994 Trinity-San Jacinto Estuary Powell et al., 2002 USA Texas Freshwater 1. Upper Lavaca Bay 1. Kalke & Montagna, Inflow methodology 2. Guadalupe & Nueces estuaries 1991 3. Sabine-Neches, Trinity-San Jacinto, 2. Montagna & Kalke, Lavaca-Colorado, Guadalupe, Mission- 1992 Aransas, Nueces, Laguna Madre 3. Montagna & Kalke, 4. San Antonio Bay 1995 5. Nueces Marsh 4. Montagna & Yoon, 1991 5. Alexander & Dunton, 2002, Montagna et al., 2009 USA Valued Ecosystem Component Methods 1.Loxahatchee River & Estuary. Alber, 2002 1.Environmental flows 2.Caloosahatchee Estuary 1.SFWMD, 2001 as cited in for indicator species. 3.Suwannee River Estuary Alber 2002 2.Use of SAV to deter- 2.Doering et al., 2002 mine minimum and maximum flows. 3.Mattson, 2002 3.Environmental flows for target habitats. China Protection of critical Yangtze River Estuary Sun et al., 2009 habitat Zhao et al., 2009 Australia Determining flows for Gladstone harbour and Cape Halliday & Robins, 2007 fisheries Capricorn Australia Determining flows for Fitzroy, Calliope and Boyne River Robins et al., 2005, fisheries estuaries Halliday & Robins, 2007

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Table A.2. Examples of holistic ecosystem methods and frameworks used to determine the environmental water requirements of estuaries

Country Method Estuary Reference UK Risk Assessment UK estuaries Binnie et al., 1998 Approach

Australia Risk Assessment Lake Condah and Darlot Creek the major Gippel et al., 2008 Approach tributary of the Fitzroy River, Australia

China Risk Assessment Jiaojiang and Lingjiang estuaries Gippel et al., 2009b approach

South Resource Directed Orange, Olifants, Palmiet, Breede, Great Department of Water Affairs Africa Measures Method / Brak, Goukamma, Knysna, Swartvlei, and Forestry reports. Ecological Reserve Keurbooms, Matjies, Sout, Tsitsikamma, Adams et al., 2002, Taljaard Method Kromme, Seekoei, Sundays, East et al., 2004 Kleinemonde, Nahoon, Mtata, Mhlanga, Mdloti, Thukela, Siyaya, Mhalthuze, Nhlabane, St Lucia estuaries Australia National River 1. Richmond River Estuary 1. Peirson et al., 2002. Health Programme 2. Emigrant Creek 2. Bishop et al., 2001 approach 3. Hawkesbury Nepean River and 3. Cox & Peirson 2003 estuary, 4. Bishop 2005 4. Lower Hastings River 5. Boyes 2006 5. Shoalhaven Australia Benchmarking & 1. FitzRoy River Estuary 1. Brizga et al., 2002 risk assessment 2. Burnett Basin 2. Brizga, 2000; Brizga et al., ELOHA 3. Barron Basin 2000 Ecological Limits 4. Pioneer Valley 3. Brizga et al., 2001a, 2001b of Hydrological 5. Condamine-Balonne Basin 4. Brizga et al., 2001c, 2001d Alteration 5. DNR 2000 – Queensland 6. Logan Basin, Mary Basin, Burdekin Basin 6. Arthington et al. 2006 Australia FLOWS Werribee & Gellibrand estuaries Sherwood 1983, Sherwood Victoria et al. 2005, Hardie et al. 2006, Lloyd et al. 2008 Australia BAFFLER, Wilson & Torbay estuaries Close 2005, 2007 (Bayesian Adaptive Framework for FLows to maintain Estuarine Resources) USA Ecological 1. Apalachicola River and Bay, Gulf of 1. Richter et al. 2003, 2005 Sustainable Water Mexico, Florida 2. Richter et al. 2006 Wrona Management, 2. Savannah River- floodplain-estuarine et al. 2007 ESWM framework system and adaptive management of Thurmond dam.

28 Environmental water requirements for estuaries

Table A.3. Examples of modelling studies used to determine the environmental water requirements of estuaries

Country Method Estuary Reference USA Numerical Lavaca-Tres Palacios Estuary and the Bao & Mays, 1994 modeling Matagorda Bay system, Texas USA Numerical Pascagoula River & Estuary Harza, 1995, Riecke, 2002, modeling cited in Peirson et al., 2002. USA Bioenergetic Lavaca-Colorado Estuary Hae-Cheol & Montagna, 2009 model Australia Numerical Derwent Estuary, Tasmania Davies, et al., 2002 modeling Australia Hydrodynamic- Swan River, Australia Chan, et al., 2002 ecological numerical model Australia Simple Estuarine Brunswick River estuary- New South Baird, et al., 2001 Response Model, Wales, Huon River estuary- Tasmania, SERM Maroochy River estuary- Queensland, Port Phillip Bay- Victoria, Wilson Inlet- Western Australia Gippsland Lakes Australia Simple flow and Swan River, Western Australia Kurup, et al. 1998 salt models China Salinity, fresh- Haihe, Zhangweixin, Luanhe estuaries Sun & Yang, 2004 water inflow relationships Portugal Ecohydrology Guadiana Estuary, South Portugal Wolanski et al., 2006 model France Hydrographic, Seine River Estuary Even et al. 2007 biogeochemical and hydrodynamic linked models Senegal Hydraulic, Senegal River floodplain and estuarine Duvail & Hamerlynk, 2003 hydrodynamic areas modeling, GIS & decision support China Water cycle, bio- Haihe River Basin: Haihe, Luanhe, and Yang et al., 2005 logical cycle, and Zhangweixin estuaries habitat water requirements

29 Ramsar Technical Reports

Ramsar Technical Reports are designed to publish, chiefly through electronic media, technical notes, reviews and reports on wetland ecology, conservation, wise use and management, as an information support service to Contracting Parties and the wider wetland community in support of implementation of the Ramsar Convention.

In particular, the series includes the technical background reviews and reports prepared by the Convention’s Scientific and Technical Review Panel (STRP) at the request of the Contracting Parties, which would previously have been made available in most instances only as “Information Papers” for a Conference of the Parties (COP), in order to ensure increased and longer-term accessibility of such documents. Other reports not originating from COP requests to the STRP, but which are considered by the STRP to provide information relevant to supporting implementation of the Convention, may be proposed for inclusion in the series. All Ramsar Technical Reports are peer-reviewed by the members, observers and invited experts appointed to the STRP.

Ramsar Technical Reports

No. 1. 2006 Guidelines for the rapid assessment of inland, coastal and marine wetland biodiversity (CBD Technical Series No. 22) (also available in French and Spanish) No. 2. 2006 Low-cost GIS software and data for wetland inventory, assessment and monitoring (also available in Spanish) No. 3. 2006 Valuing wetlands: guidelines for valuing the benefits derived from wetland ecosystem services (CBD Technical Series No. 27) (also available in French and Spanish) No. 4. 2010 A Framework for a wetland inventory metadatabase No. 5. 2011 A Framework for assessing the vulnerability of wetlands to climate change (CBD Techni- cal Series No. 57) No. 6. 2012 Healthy wetlands, healthy people: A review of wetlands and human health interaction (published jointly with the World Health Organization) No. 7 2012 Ramsar Wetland Disease Manual: Guidelines for Assessment, Monitoring and Manage- ment of Animal Disease in Wetlands (published with the Wildfowl & Wetlands Trust (WWT)) No. 8 2012 Waterbird flyway initiatives: outcomes of the 2011 Global Waterbird Flyways Workshop to promote exchange of good practice and lessons learnt (published jointly with AEWA, CMS and EAAFP secretariats) No. 9 2012 Determination and implementation of environmental water requirements for estuaries (CBD Technical Series No. 69)

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