Factors affecting water plant recovery - A. Overview and sediment influences author: J. Schutten' co-authors: A.J. Davy-,F.J.Madqwick-, H. COOpS3, W. Admiraal', E.H.R.R.Lammens3, G.L. Phillips>
Project No LIFE92-3/UKl031 RIZA project EHS*WATERPLANT ISBN 0948119403
'University of Amsterdam, ARISE, Department of Aquatic Ecotoxicolgy, Kruislaan 320, 1098 SM, Amsterdam, The Netherlands 2University of East Anglia, School of Biological Sciences, NR4 7TJ, Norwich, UK 3RIZA (Institute for Inland Water Management and Waste Water Treatment), P.D. Box 17, 8200 AA, Lelystad, The Netherlands 4The Broads Authority, Thomas Harvey House, 18 Colegate, NR3 1BQ, Norwich, UK 5Environment Agency (former National Rivers Authority), Cobham Road, IP3 9JE, Ipswich, UK
This report should be cited as: Schutten, J. Davy, A. J., Madgwick, F.J., Coops, H., Admiraal, W., Lammens, E.H.R.R., and Phillips, G.L. (1997) Factors affecting water plant recovery - overview and sediment influences. In Madgwick, F.J. & Phillips, G. L. (eds) 'Restoration of the Norfolk Broads - Final Report', (BARS14) Broads Authority and (P-89) Environment Agency, Norwich UK.
Commissioning Organisations: Broads Authority, Thomas Harvey House, 18 Colegate, Norwich, Norfolk, NR3 1BQ, UK Tel: +44 (0) 1603610734 Fax: +44 (0) 1603765710 Environment Agency, Kingfisher House, Goldhay Way, Orton Goldhay, Peterborough, PE2 5ZR, UK Tel: +44 (0) 1733371811 Fax: +44 (0) 1733231840
©European Commission, Broads Authority, RIZA and Environment Agency 1997. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior permission of European Commission, The Broads Authority, RIZA and the Environment Agency.
Statement of Use: This project was commissioned to develop novel techniques to assist in the restoration of shallow lakes. This report provides results of the 'Water plant recovery' research project from 1993 until 1995. The 'Water plant recovery' project aims at finding causes for delayed recovery of aquatic plants in shallow biomanipulated lakes, and designing management answers.
Research Partners: This document was produced by The Broads Authority, RIZA WSE, Environment Agency Broads Research Team, University of Amsterdam ARISE (Department of Aquatic Ecotoxicology), University of East Anglia School for Biological Sciences (Population Biology Sector).
Funding Organisations: European Commission, Broads Authority, RIZA, National Rivers Authority (now Environment Agency).
Project Leaders: The Broads Authority's Project Leader: Jane Madgwick RIZA's project Leader: Dr. Hugo Coops The Environment Agency's Project Leader: Dr. Geoff Phillips - Anglian Region Figure 1: Map of the Broads area, showing the position of the Broads monitored in 1993. ~
North o I mile I I o I kilometre f------
NORFOLK
The Broads
Great Yarmouth
I Alderfen Broad 2 Belaugh Broad 3 Cocks hoot Broad 4 Cromes Broad 5 Hickling 6 Hoveton Great Broad 7 Martham Broad North 8 Ormesby Broad 9 Pound End Broad AI43 10 Upton
AI46 SUFFOLK
4 Contents
6 Summary 6 1. Introduction
8 2. Environmental factors influencing submerged macrophyte distribution 8 2.1 Field survey in 1993 8 2.2 Field survey in 1995
17 3. Effects of sediment chemistry and physical properties on submerged macrophyte survival and growth 17 3.1 Experiments with transplanted sediments in a clear-water lake
18 3.2 Effects of sulphide on the survival and growth of 3 species of submerged macrophytes in a microcosm experiment
33 4. Effects of sediment chemistry and physical properties on susceptibility of submerged macrophytes to physical disturbance 33 4.1 Correlative survey in 20 shallow lakes in the Netherlands and the Broads 34 4.2. Effects of natural and artificial sediments on uprooting resistance and root and shoot growth in a microcosm experiment
35 5. Synthesis, management implications and future research requirements
43 6. References FACTORS AFFECTING WATER PLANT RECOVERY - A. Overview and sediment influences
This project was jointly financed by the EC-LlFE- Summary fund and RIZA (Netherlands) with the co-operation Nutrient reduction and biomanipulation are of the University of Amsterdam, University of increasingly used as tools to re-create clear water East Anglia and the Environment Agency. in turbid, green, eutrophicated shallow lakes. The next step, stabilising the resulting aquatic community so that fish can be re-introduced, depends heavily on the recovery of the 1. Introduction submerged aquatic vegetation, as shown for Water managers in the Netherlands (Hosper, 1993) example in other reports in this LIFE-series.This and Great Britain (Broads Authority, 1993) aim to project has sought to discover the reasons for restore clear and diverse lakes in currently algal- the varying performance of macrophytes in dominated systems.Water clarification by nutrient different lakes, and to translate the findings into reduction alone takes a long time becauseof management advice. feedback processeswhich stabilise the turbid state (Hosper et al., 1992, Scheffer et el., 1993; Moss, Experience in The Netherlands and the United 1990). In order to speed the recovery process, Kingdom (Norfolk Broads) has indicated that dredging and manipulation of the fish population lakes with a firm and mineral sediment usually have been used (Broads Authority, 1993; Hosper & have a successful recolonisation of aquatic Meijer, 1993). Macrophytes themselves seem to macrophytes, in contrast to the slow and erratic play an important part in the recovery processand recovery in lakes with a soft and organic in the stabilisation of the final clear water stage sediment. An initial survey in 1993 suggested (Blindow et al., 1993; Carpenter & Lodge, 1986; that light, nutrients and propagule availability Scheffer et al., 1993). were not the main limitations. Hence we have focused on the sediment as a limiting factor for Beds of submerged and floating macrophytes macrophyte recolonisation. A combination of provide structure to the water layer and field and glasshouse experiments showed that separate it into different habitats (Den Hartog & the sediment was not inimical to the introduced Van der Velde, 1988; Lillie & Budd, 1992), so propagules, but that high sulphide providing attachment surfaces for sessile concentrations in the sediment seem to impair zooplankton, macro-invertebrates root extension. A 20-lake survey in 1995 showed (Lewandowski, 1983) and periphyton (Carpenter that wind exposure and sediment cohesion were & Lodge, 1986; Den Hartog & Van der Velde, the main factors determining the abundance 1988; Pandit 1989; Rabe & Gibson, 1983). The and diversity of the aquatic community. Fertility macrophyte zone is also a refuge habitat with and alkalinity of both sediment and water were lower predation risk (Lubbers et al., 1990; Rozas of less importance. & Odum, 1988) for different animal groups such as Cladocera (Savino, 1982; Perrow et el., 1997), macro-invertebrates (Beckett et aI., 1992; Heck & The aquatic plant community in lakes with a firm Timothy, 1981), fish fry and young of the year sediment consisted of a combination of firmly fish (Chapman & Mackay, 1984; Grimm, 1991; rooted perennials and annuals whereas in lakes Holland & Huston, 1984). Macrophytes can with a soft sediment in the Broads, the plant indirectly improve the water quality by community consisted of only functional annuals competing for nutrients with limnetic algae that were nearly all easily uprooted. This implies (Blindow et al., 1993; Jorga & Weise, 1979), and that plants in a soft sediment lake are very restricting water-flow so suspended material can vulnerable to physical disturbance such as from settle (Gregg & Rose, 1982; Kemp et al., 1984). wind-induced currents, or bird or fish grazing, The macrophyte roots can improve sediment because of the combination of the reduced root characteristics by preventing erosion and system and the soft sediment. Once dislodged, detoxifying the sediment through oxygen release the whole plant is lost from the aquatic (Blindow et al., 1993).,1naddition macrophytes can community. Plants in lakes with a firm and be a food source for macro-invertebrates, fish cohesive sediment break before being uprooted, (Carpenter & Lodge, 1986) and birds (Carpenter & which leaves a rootstock for the plants to Lodge, 1986; Jupp & Spence, 1977; Kiorboe, 1980; regrow from. In the next stage of this project we Perrow et ai, 1996b; Schutten et al. 1994) plan to investigate how to overcome, in a practical way, the unsupportive nature of some Recent biomanipulation work in European sediments, and how to predict in a given lake shallow lakes shows that the recovery of the probable stability of its recovering vegetation in terms of abundance and species macrophyte community. diversity appears to be rather unpredictable, this is particularly so in the Norfolk Broads. That is why this 'Macrophyte Recovery Project' was 6 developed as a part of the LIFE programme growth or winter-survival. Root length may 'Restoration of the Norfolk Broads' and RIZA's increas with nutrient depletion in the sediment 'EHS-waterplant'. It is a research project that (Mantai & Newton, 1982; McFarland et el., 1992). aims to gain knowledge of the main factors High nutrient availability increases shoot/root controlling macrophyte recovery after or during ratios in Phragmites australis (Boar et el., 1989) large-scale management of shallow eutrophic and arable crops (Salisbury & Ross,1985). lakes. A scientific understanding of the limitations for macrophyte recovery will assist in 4. Herbivory. Grazing, by birds can assist water the identification of management prescriptions. plant establishment by dispersal or stimulated The literature suggests several possible growth (Belsky, 1986; Owen, 1980), or it can be limitations of macrophyte recovery. deleterious (Carter & Rybicki, 1985; Lauridsen et el., 1993; Van Donk et el., 1994). Herbivorous Limited numbers of propagules germinating birds can consume a considerable part of the maximum standing crop (Jupp & Spence, 1977; Lack of regeneration can be the result of an Kiorboe, 1980; Perrow et el., 1996; Schutten et exhausted seedbank, or adverse conditions for el., 1994) although recent research has shown germination. Field observations of extensive that in a typical broad predation by herbivorous germination in the first year after suction-dredging waterfowl is negligible during spring (Perrow et (Madgwick, pers comm.) and research on seedbanks el., 1996). Herbivorous fish such as carp, rudd, (Pitt & Pillips, 1994; Handley, 1995) suggests that roach (Prejs, 1984) are not abundant in the in the Broads the seedbank is not wholly Broads, but benthic feeding of bream and tench exhausted, and it is likely to be supplemented (Carpenter & McCreary, 1985; Ten Winkel & from adjacent vegetated upper reaches of the Meulemans, 1984; Wright, 1992) could have an river (Kennison & Prig more, 1994) and marsh- impact on macrophyte recovery. dykes (Doarks et el., 1990) by water flow and waterfowl. Research elsewhere has not shown Aims and objectives. any clear correlation between seedbanks and present vegetation (Kautsky, 1990; Skoglund & Given the wide range of possible interacting Hytteborn, 1990; Smith & Kadlec, 1983). Seeds mechanisms it was necessary to focus the project tend to be more dense than the sediment so on the most important ones. A pilot study in they sink, and may not germinate if they are 1993 led to the conclusion that the sediment buried too deeply, because they do not receive chemistry and physical properties were most the appropriate environmental cues for likely to be involved in limiting submerged germination (e.g. light) (Bartley & Spence, 1987; macrophyte recovery in the clear water broads Forsberg, 1965; Muenscher, 1936). with highly organic sediments. This work is presented in section 2.1 Limited growth and survival The current project connected the RIZA research Growth may be limited by a number of factors project "EHS-Waterplanten" with the joint (Duarte & Kalff, 1990; Westlake, 1975): Broads Authority/NRA project supported by the EU LIFE.The Universities of Amsterdam and East 1. Light. Biomanipulation, in the form of nearly Anglia were also active partners in the project. complete removal of zooplantktivous fish, has Thus this report covers the research carried out been carried out in the Netherlands and the between 1993 and 1995. Broads in severely eutrophicated lakes; this has resulted in clear water and yet macrophyte The sequential research questions were: recovery has not always followed. In such cases, 1. How do the distribution and abundance of low light and nutrients resulting from enrichment submerged macrophytes change through the can be excluded as limiting factors. Pilot research season in contrasting lake types? (chapter 2) has shown that the plants in the Broads 2. What are the most important environmental are not excessively covered in epiphytic algae. factors affecting submerged macrophyte species distribution and abundance (e.g. light, 2.Water flow can enhance growth by reducing periphyton cover, sediment density and grazing). precipitation of particulate matter on leaves or 3. What is the influence of sediment chemistry by reducing boundary layers that resist diffusion on survival and growth of submerged of oxygen and bicarbonate (Scheffer et el., macrophytes under natural conditions in the 1992). However water-current induced forces absence of herbivory? can also uproot the plants. 4. What are the specific effects of possible toxic levels of sulphide in the sediment on the survival 3. Sediment quality. Unstable sediments may and growth of selected submerged macrophyte induce high mortality (Rorslett, 1985). Toxicity is species under glasshouse conditions? likely to be a problem for submerged 5. What are factors affecting plant resistance to macrophytes in the highly organic Broads uprooting under natural and controlled conditions? sediments (Barko & Smart, 1983; Smolders & The overall aim was to design protocols for to Roelofs, 1993). Particularly high levels of the management of macrophyte recovery in the sulphide (Pulich, 1985; Koch et el., 1990) and field. ammonium ions (Roelofs, 1991) can reduce root 2. Environmental factors influencing submerged macrophyte distribution 2.1. Field survey in 1993 The results of the multivariate analysis (Figure 3) suggest that sediment type and physical Aim properties are major factors explaining submerged macrophyte distribution in the To characterise species distribution and Broads (54 % of species / environment relation abundance and their changes through the explained by the first axis (Monte Carlo season; to estimate the influence of light, Permutation test, n = 99, P = 0.01). Water colour periphyton cover, sediment density and grazing and light penetration were of less importance. on the distribution and abundance of submerged macrophytes. Conclusion
Methods The 1993 survey showed that the submerged Ten Broads (Upton, Pound End, Ormesby, macrophyte community changed considerably Martham-North, Hoveton Great, Hickling, during the growing season in terms of species Crom.es, Cockshoot, Belaugh and Alderfen, abundance and dominance. The plant see Figure 1) were surveyed, during this pilot communities in the Bure broads differed study,on four occasions (end of April, end of significantly from those in the Thurne area, and June,.early August and mid October) during the this appeared to be associated with sediment growing season. The abundance of plant species type and structure. Light and periphyton cover was estimated as vertically projected bottom were not the main factors limiting submerged coverage on three representative transects from macrophyte growth or recovery in the lakes shore to shore by snorkel diving. The abundance examined. was recorded using a 7-point Tansley scale (Schutten et al., 1994). A visual estimate was These results suggested focusing the made of periphyton cover, plant colour and 'Macrophyte Recovery Project' on sediment- vigour, and basic limnological parameters were related parameters. measured (water temperature and depth, Secchi depth). The top layer of the sediment was 2.2 Field survey in 1995 sampled using a 35cm perspex manual corer (diameter 7 cm) and visually classified in Aim sediment type based on colour and density. The aim of this survey was to determine on a Multivariate analysis, using a unimodal response wide geographical scale, the most important model (CCA, CANOCO, Ter Braak, 1994) with rare environmental factors controlling submerged species downweighted, was carried out to macrophyte species distribution and abundance· correlate species abundance and environmental to determine the effects on particular species in' variables. contrasting types of lake.
Results Methods There were large changes in the abundance and The distribution and abundance of submerged dominance of submerged macrophytes during macrophytes was examined, and a range of the growing season. The small Bure broads, with environmental factors relating to sediment and very fluid sediments, possessed sparse vegetation water were sampled in 20 shallow lakes in The dominated by filamentous algae in spring and Netherlands (Figure 4) and the Broads (Figure 1) low abundances of superficially rooted and in July and August 1995 easily uprooted species during the rest of the season (e.g. Belaugh Broad, Figure 2a). The The submerged macrophyte community was larger and more saline Thurne broads, with firm sampled at 2 or 3 locations, that differed in wind sediments, had diverse, strongly-rooted exposure, in each lake. Th'e abundance of each submerged communities with highly abundant species was estimated as vertically projected perennial species early in spring (e.g. Martham bottom coverage on a 10 x 10m quadrant by North Broad, Figure 2b). The periphyton and snorkel diving. The abundance was recorded turbidity data (not presented) from the clear using a 7-point Tansley scale (Schutten et el., broads suggest that the submerged macrophyte 1994). A visual estimate was made of periphyton community was not limited by water clarity or cover, plant colour and vigour. Basic limnological epiphytic algal growth. parameters including water and sediment temperature, pH, REDOX, and water depth and Secchi depth were measured and fetch (distance
8 from the shore in the prevailing wind direction) Results was estimated. The sediment pore water and Multivariate analysis suggested that wind lake water were anaerobically sampled using influence and sediment density were primary Rhizon samplers (10 cm long microporous Teflon factors and sediment and water alkalinity and filter tubes, pore diameter 21Jm,connected to an nutrient status were secondary factors explaining evacuated sampling container). The force submerged macrophyte distribution (19 % of needed to perturb the top layer of sediment species / environment relation was explained by (shear force) was measured in situ using a pocket the first axis and another 15 % by the second shear meter (Torvane, ELE-international). The top axis; Monte Carlo Permutation test of whole layer of the sediment was sampled using a 35cm analysis for n = 99, P = 0.03). perspex manual corer (diameter 7 cm) and visually classified into layers on basis of colour, The species were clustered using TWINSPAN (Hill, density. Ionic concentrations of the pore and 1994), which resulted after two divisions in the lake waters were analysed using Atomic following clusters: Table 1. Absorption spectrometry for the cations (Fe, Mn, Cu, Mg, Ca, K, Na) and Ion-chromatography for The species clusters were graphically correlated the anions (Cl, N0 , N0 , P0 , S04)' Sul~hide and 3 2 4 to the most important environmental factors ammonium were preserved and determined which showed that clusters 2 and 7, the non- within one week using ion-selective electrodes. rooted, floating leaved and Najas marina tended The sediment dry-weight (105 QC)and loss-on- to be present on less wind exposed locations ignition (550 QC,2 hrs) were measured. than the other clusters (Figure Ga).The mean Multivariate analysis correlating species shear force of the sediment (Figure Gb) increased abundance to the measured environmental from cluster 2 to cluster 6 indicating that the variables, was carried out using a unimodal more rooted species were present on the more response model (CCA, CANOCO, Ter Braak, 1994) stable sediments. Clusters 1 and 7 were present with rare species downweighted. on the whole range of sediment stabilities.
Conclusion The 1995 survey suggested that the submerged macrophyte species distribution was mainly governed by wind influence and sediment stability, and secondarily by sediment, water alkalinity and nutrient status.
Table 1: Twinspan clusters of the 1995 survey data. number group species 1 Floating-leaved species Nymphaea alba, Nuphar lutea, Nymphoides peltata 2 Non-rooted and Utricularia vulgaris, Lemna minor, L. trisulca, floating leaved species Ceratophyllum demersum. Myriophyllum verticillatum, Potamogeton natans, P.obtusifolius, Ranunculus circinatus, Stratiotes aloides Fontinalis antipyretica and Elodea nuttallii were only found once. 3 Algae group with Filamentous algae, Enteromorpha intestinalis with Zannichellia Zannichellia palustris 4 Rooted species Potamogeton pusillus, Elodea canadensis 5 Strongly rooted species Potamogeton perfoliatus, P. lucens, P. crispus, Hippuris vulgaris the fragile Callitriche spec. and the Charophyte Nitellopsis obtusa 6 Narrow-leaved species Potamogeton pectinatus, P. mucronatus, M spicatum, Ruppia maritima and the Charophytes Chara aspera and C. connivens 7 Najas marina Najas marina [ -
8
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'13 .•cO.... C\l "'0 >. (l) •>.... :::::l 3~,------~------, III Pobtu Lf) .•. m m..- ..(l)c .•.... '+- 0 2 •III.... .•0.... u C\l '+- Hvulg C\l .•. .•.... Calli C Nitel (l) .•. .•. E 1 Pperf c Fe-w .•. •0.... > c Shear (l) Ecan "'0 .•. C MaxI C\l (l) 0~ ~~N:H:Mvert4-..S~•• Na:lb~"'~Mn~ . Ppec-=-".•• U "'--='=91 ~~I Fetch (m, 2*SE) N W ...j::;:. VI 0\ 0 0 0 0 0 0 ZO 0- 0 0 0 0 0 I I I ---L- I ~ 11 I ~ ::s-. I r:J) ~ N § - N ~. (j I ~ r:J)- t"""+ (D ~ N -~.l I I L------¥----- I i Figure Gb. Abundance of submerged macrophyte clusters related shear stress (force needed to perturb the top layer of the sediment). Shear stress top 5cm (g, 95%CI) -....J W 0 I I ! I +;:. ~1 I VI ~j I I I 0'1 U11 N I I I 16 3. Effects of sediment chemistry and physical properties on submerged macrophyte survival and growth Experiments were performed on three species of exclosure in Alderfen Broad. The five treatments submerged macrophytes that are rapid colonisers were sediment transported from elsewhere in and widespread in both the Netherlands and the Alderfen, in situ Alderfen sediment, in situ United Kingdom: Alderfen sediment without protection against fish, sediment transported from Ormesby and Ceratophyllum demersum is usually free-floating artificially fertilised coarse sand. The containers in the water layer, although parts may be loosely were buried in the Alderfen sediment with only buried in the top layer of the sediment. It has no the top 5cm protruding. Five replicate containers roots, but underground parts can act as were planted with each 9 vegetative propagules absorption sites (Pond, 1903). Sediment would be (10 cm stem-tips with at least one node for expected to have little influence on growth and C. demersum and E. canadensis, or 1 shoot with development. roots and rhizome section for Z. palustris) of one the 3 species. Five containers were left empty as Elodea canadensis is a rooted plant that can a control for colonisation. All containers, except absorb nutrients from both the water layer and the unprotected in situ sediment were covered sediment (Pond, 1903; Weeda et el., 1991). with 5cm plastic mesh to prevent fish affecting Influence by the sediment and water would be the plants. Shoot lengths, and water and expected. sediment chemical properties (see 2.2) were measured on a 3-weekly basis until the middle Zannichellia palustris is a rhizomatous rooted of October. plant that absorbs nutrients entirely from the sediment (Pond, 1903; Weeda et el., 1991) and Result - 1994 experiment thus large influence of the sediment would be expected. The growth of the three species on the five sediments is shown in figures 9a, 9b and 9c. 3.1 Experiments with transplanted Statistical analysis (ANOVA for each sampling sediments in a clear-water lake date) of the shoot lengths showed no significant effect of the various sediments on C.demersum Aim after the turbid period (Figure 9a and 10) caused by a persistant blue-green algal bloom. To test the relative importance of sediment C. demersum colonised from 10 August onwards chemistry on survival and growth of the 3 on all sediments. E. canadensis died quickly on submerged macrophyte species. the brackish Hickling sediment, but there was no significant difference between the other Method - 1994 experiment. sediments. Strangely only one individual invaded In May 1994, 12 containers (18 I) of sediment and this was on Hickling sediment. Z. palustris from each of 5 different broads (Hickling, survived the best on Cockshoot sediment, grew Alderfen, Cockshoot, Hoveton Great and Pound reasonably well on Cockshoot and Pound End End) were transported to the bird-free exclosure and Alderfen sediment. Only one plant colonised in Alderfen Broad (figure 8). The containers were Cockshoot sediment. buried in the Alderfen sediment with only the top 5cm protruding. Three replicate containers Analysis of the sediment chemistry data gave no per sediment type were planted each with 9 apparent explanation for the observed vegetative propagules (10 cm stem-tips with at differences. pH and REDOX measurements (not least one node for C. demersum and E. shown) and field observations showed that canadensis, or 1 shoot with roots and rhizome experimental artefacts such as transient section for Z. palustris) of one the 3 species. oxidation and acidification associated with Three containers (one per sediment type) were transportation of the sediment, the effect of left unplanted as a control for colonisation. resting young perch, and very limited light Shoot lengths, and water and sediment chemical conditions in Alderfen because of a persistent properties (see 2.2) were measured on a 3- blue-green algal bloom, had more effect on the weekly basis until the middle of October. plant performance than the sediment itself. Colonisation of the control containers by C. demersum (and one plant of E. canadensis Method - 1995 experiment and Z. palustris) after the turbid period showed In May 1995, 20 of the same (see 1994) the weak influence of the sediment and that containers were used for each of five different these species were able to disperse. sediments, and transplanted into the bird- 1995 experiment Method The growth of the three species on the five Two consecutive experiments were carried out in sediments is shown in figures 11a, 11b and 11c. the greenhouse of the UEA during the summer of 1995. Four replicates of the four sulphide The 1995 results for C. demersum show growth concentrations (0, 300, 600, 900 I-lM sulphide) and survival on all sediment types. Statistical were maintained in the sediment compartment analysis of the results for each sampling date of the tanks (Figure 12), whilst the overlaying show no significant difference between the Alderfen surface water was the same for all of treatments. C. demersum colonised all sediments the treatments. Ten shoot tips of the 3 species during the experiment. Analysis of E. canadensis were planted in each tank so that 5 cm was lengths in 1995 show significantly longer plants below the rubber membrane. Shoot length was on Alderfen or Ormesby sediment than on measured weekly. Sediment pore water and tank fertilised sand on 9 June and 4 July. There was water were sampled weekly using Rhizon no significant difference in growth or survival of samplers and analysed for anion and cation plants grown in transplanted sediment or in content (see 3.1). Shoot and root length and plots protected against fish predation compared biomass were harvested in each tank. After poor with the control plots. E. canadensis did not growth in the first experiment it was repeated colonise any sediments during the 1995 with ortho-phosphate addition to the sediment experiment. Analysis of Z. palustris lengths compartments to mimic the natural nutrient-rich showed no significant difference between the conditions in the broads sediments (referred to sediments. Z. palustris colonised on all as experiment 1 and experiment 2 respectively). sediments, but was most successful on Ormesby sediment. Z. palustris is a common species in Results Ormesby, so propagules were probably present in the transplanted sediment. This can explain The growth of the two species grown on the the high recruitment of plants. different treatments are shown in Figures 13a, 13b, 14a and14b. Unfortunately Z. palustris did not grow on any of the sediments. C. demersum Conclusions plants did not differ in length during the These experiments show that C. demersum is not beginning of experiments. However at the end sediment-dependent, and can grow on all of the experiment plants grown on sediment sediment types used. The species is however very with added sulphide were longer than grown on mobile, even within one growing season. E. sediment without sulphide. E. canadensis plants canadensis showed poor survival and growth on grown with or without sulphide addition in the Hickling sediment, but was able to grow well on sediment did not differ in length. There was a Alderfen, Hoveton Great, Pound End and trend (not shown) that the highest sulphide level Cockshoot sediments. Z. palustris had the lowest number of roots compared with grew well on Cockshoot, reasonably well on other treatments. All plants in experiment two Pound End, Ormesby and Alderfen sediments were longer than in experiment one, which but not on Hickling sediment. These two showed the effect of the fertilisation with experiments show that only the brackish Hickling phosphate. sediment can restrict growth and survival of the 3 species tested. Conditions in the water (light, Conclusion algae) during the course of the experiments were more important than the nature of the The main conclusion is that at the concentrations sediment. The sediments used were not able to used, sulphide was not restricting the presence limit colonisation of C. demersum. and growth of the sediment-independent C. demersum or the partly sediment- dependent E. canadensis. There was a clear stimulatory effect 3.2 Effects of sulphide on the survival of phosphate fertilisation in the sediment and growth of 3 species of submerged compar-tment on the growth of E. canadensis. Z. macrophytes in a microcosm experiment. palustris did not grow on any of the sediments. Aim To test the effect of possible toxic levels of sulphide in the sediment on the survival and growth of three submerged macrophytes. 18 Figures 7a, 7b & 8. Figure 7a: Photograph of C. demersum Figure 7b: Photograph of E. canadensis (Schutten, 1996) (Schutten, 1996) Figure 8: Photograph of bird-free exclosure in Alderfen Broad (Schutten, 1996). 19 Figure 9a. Mean shoot length (and 95% Confidence Interval) of planted C. demersum, grown on 5 different sediments in a bird-grazing protected environment in Alderfen Broad during the summer of 1994. shoot length (cm, 95%CI) ~ I\.) W 0 0 0 z 0 en 11 W ro 3 0 ....• +, '"0 ~ ....• _. I '" L ....• ::J c '" (C :::J 0>'" 0. CD .r...o• ,1 .-+w "-, -, I\.) ~ f--- ,~ CD I eo . ~--,--"-.-~ <0 I -, L .". -, C <, :::J .". ,'~---j <, ~ h-C- CD 01 \ \ ~ \ "'I \ 0 01 I » '" \ C cc /*' \ 0 ~~ / I -j- I I\.) '" ~- 01 '" , ,- --~ I I ~ ~ I c» .". / cc -~ - 0> 1--, - ~~- /' /' /' /' /' I\.) /' »: 01 • I Cl) W CD ,/' "'0 .". H~ \ ~ '" cc ~ I 0 o .". ~ r-+ .". f-- I Cl) f-----i r--j ~I f-----j f-----j f-----j CD ~I -/ -/ +; a. '"U II o » 3 0 o 0 0 a. CD c ~ < o :::J :::J CD ~ CD r-+ a. r-+ en :::J 0 zr ~ CD cc :::J :::J :::J 0 a. G) r-+0 OJ 20 .•... N +-'o::i CO'I Q)O'I •....•... Q),+- ~ 0 25 I I -0 •... Ln Q) C E o E C ~ T Sediment o3':..Q)c •..• +-' 0'10'1 20 ",' C 'Vi 'c I c: :::J Q)-O "'0-0 --.- -Alderfen III III c: 0 III •... /\ Vco L.I,j C 15 -0 Q) T Q)'t I / \ +-' Q) ~ C-o ~ /; \/ }\ \\ -.- Cockshoot Ill- m c..« U '+- C \ -. \ \ o "- ~ / ..•..•C+-' IJI 1 n; Q) 0\ 10 \ \~ ~ E •... Q) C \ \ ~ --Hoveton GB +-' 0 \ /( C•... 8 ~ 's o \ T u C Q) '-" l-. C <, Q)-o '~- <, I -0 Q) '+"-- +U-' I t 5 I C Q) r' -. - Hickling o+-, ~ U 0•... Q) "(J?Q. ~ <, LnO'1 - 0'1 C o I -0 "N o C III ...c: I1J •...... •..0'1 tr: o - T -Pound end ..c-oI +-'•..• N = 27 27 27 27 27 17 22 27 18 22 6 4 9 15 537 11 I 2 2 4 122 3 c0'1.."c- Q) I1J 04-June 28-June IO-Aug 25-Aug 25-Sep 18-Gct +-' C • 0"- ..c 0 ~ en ..c C CV V"I Q) •.•• C E ::::J 11J"- sampling date Cl Q)-O u:: ~ ~ Figure 9c. Mean shoot length (and 95% Confidence Interval) of planted Z. palustris, grown on 5 different sediments in a bird-grazing protected environment in Alderfen Broad during the summer of 1994. shoot length (cm, 95%CI) 0 00 Z 11 ....N• 0 ~ ....N• • I .....• ....N• ~ ....N• (tI = ....N• ~---- -, ~~~~--~-~~ I. f-----+-.~----I ', ,J o ;; I--\--'a- ' i-'. I -> - \" I ~ "\ .> (JQ ,>;.' // , / IV / / Vl 0- ~--'--tIt-~ I > - " / ~ /" (JQ IV Vl N 1------"\ " I o: "\ ' (tI "\' '"0 '. ------..-;rI~-~,------1 '\ 00 •\ -I \ o \ U r- ~ (/l 1 (tI f----1 ----i .••• 1 ~I f--- .: r-----1 _.0.- -I I -I ""0 n S 0 ::c ::c > (tI (") 0 0 0.- ~ -. (") --- < (tI .=-+ ~ (tI ~ 0=.- --- .-+ Cl) '"1 -. 0 ::::r- (ti' (tI (JQ= = 0 0=.- Cl .0-+ = OJ 22 Figure 10. Water temperature and light penetration (Secchi depth) in Alderfen broad during 1994 Secchi depth (m) . 00 o N •....• •....• I E: •.I...• '-0 '-0 +:- •....• 0 I io (l) '"Cl •....•I '-0 '-0 +:- t ~ tr: n (") (") ::r -. ••• ~ n •....• 8 0 ~ I n "'""I Z 0 < 2: •....I • "'""I '-0 ~ ~ N N w n '-0 +:- 0 VI. 0. VI 0 0 0 0 0 0 Water Temperature (OC) , 23 •.... Cl) +-' E c E ••Cl)..• on::J ~._ .. Cl)c l25T ,,+-' LI'l 01 C C .- o ~ c" 3:" ••o ...0re 01 ••... 100 • CQ E c :::J Cl) •...... ,,-•.... Cl) Cl) Sediment E~ ~«c \) .- 75 +-' ,-.., I Alderfen, no bottom "CCl) Cl) ~ +-' E c c U * or net cover ~ 0 1 1,0', 0..:: 'cf( -, I -o c> l/") I -, _Cl) '1 I '-. 0\ I Alderfen with bottom / < re" r- 50l > Cl) ••... +-' • no net cover Cl) U <, <, +-' E ,i Cl) C +-' ,,/ - 0 o Cl) ••... '-'" <, u 0. l / I C 01 I Alderfen with bottom Cl) C ".-.- N o and net cover t /' -c •.re... ~ 25 o 01 ~ U' 1 '/~;/"':::'.L /'/ /' I ~ ".= ~ .r ,»> /' Fertilised sand LI'l..o -o , 0/ /' • (J') re o ~ -: 11 "c . c- ...t:: +-e-'0'lF'if I re on en 0..1 - +-' , 0- Ormesby ..c c +-' Cl) N= 55555 5 5 5 5 5 54555 54433 5 4 1 4 3 2 1 O1E c+-' Cl) re Ol-MAY-95 09-JUN-95 04-JUL-95 02-AUG-95 30-AUG-95 lO-OCT-95 - Cl) ••• +-' ••... '" 0 +-' •••.• 0 on .•••• ..c +-' Cl) on ~ LJ1 sampling date •.. c E (J') a re·- (J') ••••• Cl),,"- u:::: ~ onCl)- 0 ' arr water layer 45 cm out flow in flow 27 ..(])c +-' s 40~i------~ VI' c 0 '';::::; •cu.. +-' e (]) u c 0 u 30 (]) "'0 ..c T II I III IS (uM) Cl. ::l VI +-' e .rL (])•...... - (]) - ~ o 0 "'0 20 ..c '::!2. • 0 +-' L() "~ ....: (J') +-'+-, I e e (]) (]) - I - i: - 300 EE E I i5 "L: 0 T I i (]) (]) -. VI Cl. oe (])X , -..--c 1 +-' 10 J 1 ell) 0> 3:~ C I "-T-- 600 •0....- Q.) O'IQj ~ E +-' o E 0 o ::l 0 ~ VI ..c E ~' Cl) o J .-- 900 :JUJ I I I I I I ~;:) N = 4039 3940 36 38 37 39 39 39 35 37 2529 27 29 25 27 27 27 22 24 22 28 2622 25 30 17 18 15 19 15 15 16 19 8 8 6 8 (]) (]) E..c (])+-' 24 29 33 , 36 39 43 46 50 54 57 ~~ o (]) t1J VI M '+- ::l ••..•0 0 Cl) ..c..c •.•• +-' e Day after start experiment :::::I 0'1 (]) C'I e (]) u:: ~ ~ 00 N cn N ..Q)c +-' 60 I I s ",- c ,Q T +-' •C\l... +-' C 50 Q) u C 0 u Q) "'0 SCuM) ..c Q. 40 ::J +'"-' -I C 1 •Q)... /lv Q) -~--- ~ • 0 "'0 U 30 ..c ;4~/-- +-' ~ 1 '~ N If) 1 +-' +-' 0\ c c Q) Q) " , ,/ - ~ - 300 EE :0 ';: S 20 L~T,"; 1 Q) Q) U '" Q. "-" ~'''::{f C x o Q) -B I c Lt) 01) ~cn ~ T 600 •O~... Q) 10 0) •... ••...... • Q) ~ E ~ .L o E 0 I o ::J 0 -5i '" ~ E <1.- r.I'J o .-- 900 :::,UJ ~::> N; 60 59 60 60 58 59 58 60 57 57 58 59 48 52 49 51 10 II 10 II 15 22 16 20 5 9 6 6 Q) Q) E..c Q)+-' 1 6 12 18 21 25 32 ~+-' C\l .0 o Q) M '+- '" ••...•0 6 Q) ..c..c Day after start experiment •••• +-' C ::::l 0) Q) C'I C Q) .- Q) •... LL ...J 0) ~ VI- e o +'ru '- 50 +'e shoot length (cm, 95%CI) >-' IV VJ ..j::::. VI z 0 0 0 0 0 0 U 11 ~ 0\ 0 ~ 0\ ~ 0 (tl >-' v- ~ 'C> ~ 0\ ir: 0 r-+- ~\ ' \ ~ 0\ 0 \\ (tl 0\ 0 ~ 0'\ v- ""d 'C> '~1\ (tl 0\ fI.{,\ -.~ 0 '\ s v- '~\ f- (tl 00 ----j '~ g v- > cl >-' 00 , , IV v- 00 ~ v- -..J " , '" v- \'~ --i N , ':\ v- >-' v- \-~ 00 v- ' , 0\ I~ v- v- ~\. c::; \f\ IV :; f ,- >-' ;:;; <11, ~ I \I c::; l" J N -..J "'11" N ~ -11>- IV -..J ----1' , VI N 1\' -..J N ,\ ~ 00 ~,--\-\ \ ;:;; \ ~ VJ N IV ;:;; \ N ill .1 f------1 ~: f-----1 _I f------1 \0 0'\ VJ o o o 0 o o o , 31 N "0 C .-IU +-' C 1500r Q) E •... ~ Q) Q. X I Q) Ol •C... ::l "0 ~In C IU +-' 1000 -Q)S ~ ~ 13In .U....•.•.0 . ~ 0 . -,-- • Q) V) treatment 0'1 ---,-- S•... IU r- E ::E I 8 ~ * OuMS +-' '-' 500 c ---r------L ----.-- -,-- E 'S I :.c Q) ~ S ® 300 uM S Q) "- -S ""C o I c Q) ---r~ o :; crJ 600 uM S ------'-- ~ § ~ .;::; .,...-4 ---L- I ~ r:/). oL_ I I \I , ~-----1-- _ • 900 uM S c ---= j " Q) N= 4 4 4 4 4 3 4 4 4 4 3 4 1 1 1 u C o u 30-AUG-95 06-SEP-95 12-SEP-95 20-SEP-95 Q) ~ J:: LI"I Q. .•••. ::l Date QJ In •.•.C ::s IU C'I Q) u:::: ~ N M / .- I 4. Effects of sediment chemistry and physical properties on susceptibility of submerged macrophytes to physical disturbance The research in this chapter seeks to link spectrometry for the cations and lon- sediment chemical and physical properties to the chromatography for the anions. Sulphide and force needed to pull a plant out of the sediment ammonium were preserved and determined as (uprooting resistance). The uprooting resistance soon as possible using ion-selective electrodes. of a plant growing at a specific site should The sediment dry-mass (105 DC)and loss-on- indicate the potential impact of wind-induced ignition (550 DC,2 hrs) were measured. currents or predation on the plant. It will either Multivariate analysis of the uproot data (not be uprooted and lost from the system or break including broken plants) using a linear model and, possibly, regrow. (RDA, Canoco, Ter Braak, 1994) was carried out to identify the most important factors 4.1 Correlative survey in 20 shallow influencing uprooting resistance. lakes in the Netherlands and the Broads Results Aim Multivariate analysis suggested a strong A correlative survey was carried out to in July relationship between the uprooting force, and August 1995 to determine the most salinity (Na+, K+), nutrients (N03-, NH/, sot, important environmental factors controlling PO/-) and shear stress of the top layer of the plant uprooting resistance. sediment (Figure 16). The significance of this relationship, using the Monte Carlo Permutation test, n = 99, was 0.08. The first axis explained Method 31% of the uprooting force / environmental The force needed to dislodge a plant from the relationship and the second axis added 25%. sediment, whether or not the plant had roots (uprooting force) and a range of environmental The major factors correlated with the uprooting factors relating to sediment and water were resistance were very variable between species measured in 20 shallow lakes in the Netherlands but species could be grouped in their behaviour (Figure 4) and the Broads (Figure 1) (see also (Table 2). In general the nutrient content of the chapter 2.1). sediment (P043-, S042-)seemed to reduce the uprooting resistance for the first three groups The uprooting force of at least three individuals that have a clear root or rhizoid system. The per species was measured on two or three uprooting resistance for these groups appeared locations in each lake that differed in exposure. to increase with the sediment stability and the A string was attached to the base of a plant and salinity. to a spring balance at the other end. Vertical force was increased slowly until the plant came C.demersum and the filamentous algae group, loose from the sediment or snapped. The force which do not produce roots, were better applied was read from the spring balance. Then anchored in lakes with phosphate-rich water, but the remaining underground parts of the plant worse in lakes with a high salinity or high (stem, root and rhizomes) in the sediment were concentrations of nitrogen compounds in excavated and the plant was stored in a sediment and water. refrigerator until the length of root and shoot and dry-mass could be measured. Basic Najas marina is an unusual species in that it limnological characteristics of water and thrives under high sulphide concentrations in un- sediment (temperature, pH, REDOX) and depth exposed water bodies with fluid, reduced and Secchi depth were measured. The fetch sediments. (distance from the shore in the prevailing wind direction) was estimated. The sediment pore Conclusion water and surface water were sampled anaerobically using Rhizon samplers (see chapter Sediment structure affects plant community 2.2). The shear force (force needed to perturb composition partly due to the vulnerability of the top layer of sediment) was measured in situ certain species to being uprooted. The results using a pocket shear meter (Torvane, ELE- show that the effects of the variables measured International). The top layer of the sediment was differ strongly between the different plant sampled using a 35-cm perspex manual corer species. This means in practice that a certain (diameter 7 cm) and visually classified into layers species can be expected to be anchored strongly on basis of colour, density and sediment type. in a certain sediment and is therefore not Ionic concentrations of the pore and lake water strongly affected by physical disturbance in that were analysed using Atomic Absorption particular situation, whereas other species can show the opposite response. 33 4.2. Effects of natural and artificial were significantly higher on the Ormesby and Pound End sediments that were used in the sediments on uprooting resistance and second experiment. However the plants were root and shoot growth in a microcosm planted deeper during the second experiment, experiment which increased available surface for nutrient absorption and resistance to being dislodged. The uprooting resistance (Figure 17b) was strongly Aim correlated to underground stem length, indicating a physical effect of the sediment. No underground To test the influence of sediment density on root growth measurements were made, so underground and shoot growth and uprooting resistance of growth could not be related to sediment type. three submerged macrophyte species under controlled conditions. E. canadensis shoots were longer and root biomass was higher on Alderfen sediment and Methods fertilised sand than in the other two sediments (Figure 18a). The uprooting resistance was Two consecutive experiments, with each four closely related to the root biomass and length. replicates were carried out under controlled The sediments could be ranked by uprooting conditions in the greenhouses at the UEA during resistance: fertilised sand> Alderfen > Pound the summer of 1995. In the first experiment End and Ormesby (Figure 18b). fertilised sand and Alderfen sediment were used, Z. palustris did not grow well on any sediment and in the second experiment Pound End and (Figure 19a), so only one harvest was done. The Ormesby sediment. Overlaying water for all force needed to uproot the plants was generally treatments was Alderfen surface water. Ten greater in the first experiment (Fertilised sand shoot tips per species were planted in 40 x 60 x and Alderfen sediment) than in the second and 40 cm cold water storage tanks which contained was closely related to root length. Plotting a 15 cm layer of sediment. Shoot length was uprooting resistance versus root length shows measured weekly and two randomly selected this relation clearly (Figure 19b). plants of each species per tank were uprooted experimentally, and the force required measured with a spring balance (see 4.1). Sediment pore Conclusion water and tank water were sampled weekly These experiments showed that uprooting using Rhizon samplers and analysed for anion resistance is strongly related to the buried length and cation content (see 2.2). of the species examined. Resistance also increased with sediment density. This means that C. demersum, the non-rooted plant, grew the under field conditions the plants with the best on fertilised sand (Figure 17a). There was no longest roots or growing in dense sediment difference in shoot length produced between would be better anchored and thus lesssusceptible the three natural sediments. The shoot biomass to uprooting by exposure or bird grazing. and uprooting resistance (Figures not shown) Table 2: Major environmental factors correlated with uprooting resistance of particular species Species strong positive factors strong negative factors lake sediment lake sediment Hippurus vulgaris, SOlo, NO/-, Na+ POl- Chara aspera, Na+, NH4+ Callitriche spec. P0 3., 52- Myriophyllum spicatum, Na+, NH4+ K+, NO/-, Na+, 4 Potamogeton pectinatus dry-mass, Ruppia maritima shear stress Potamogeton perfoliatus, fetch REDOX, dry-mass, SOl- Sulphide Potamogeton pusillus, shear stress Chara aspera Chara connivens Ceratophyllum demersum, K+, N03·, Na, shear Filamentous algae stress, dry-mass Najas marina Sulphide Fetch REDOX, dry-mass, shear stress 34 5. Synthesis, management implications and future research requirements Synthesis cause them less damage. Shoots that break from their roots can easily be replaced by regrowth This project has shown that recovery of since the roots are still present in the sediment. submerged macrophytes after biomanipulation The perennials form a matrix that facilitates the in lakes with firm sediment and clear water can establishment of annuals in spring, resulting in a be successful, and normally involves firmly stable and diverse community. This means that rooted perennial species and less firmly-rooted managers of firm sediment lakes are unlikely to annuals. The recovery of submerged macrophytes encounter serious problems with recolonisation in soft-sediment systems is usually slow and of aquatic macrophytes after biomanipulation. erratic, and consists only of loosely rooted species However managers biomanipulating soft organic that are functionally annuals. An exception to this sediment lakes will probably encounter problems rule is Najas marina. This slow and erratic recovery with the recolonisation, and the resulting is typical of the Broads which tend to lack the macrophyte community will be very susceptible firmly-rooted perennials that some of the Dutch to currents and grazing. Further research in this lakes have. Research has shown that macrophyte project should be aimed at designing techniques distribution is strongly correlated with lake size to overcome the non-supportive nature of the and sediment density, and to lesser extent with soft sediment lakes. sediment and water chemistry. The sediment chemistries of the broads investigated do not Future research appear to prevent plants from growing, but can reduce root development, and thus make the In order to stabilise the aquatic community of annuals more susceptible to physical disturbances the soft-sediment lakes with firmly rooted (currents, grazing, benthic feeding). Sediment of perennials we must know amongst other things: 'tow density does not provide a firm, supportive substrate for root systems that are already 1. Are the organic and fluid sediments of the impaired by sediment chemistry. Field evidence Broads a suitable environment for firmly rooted suggests that filamentous benthic algal mats on species otherwise tolerant to organic sediments? fluid organic sediments provide plants with a Is it necessary and practically possible to protect firmer substrate, because they tend to fix the firmly rooted species from physical disturbance sediment. The reasons for the general absence of until they are established, either by stabilising firmly rooted submerged species in the newly the sediment with geotextiles, or by protecting biomanipulated soft-sediment broads require the plants from grazing? further investigation. 2. Isthe growth of roots and shoots affected adversely by ammonium toxicity in the sediment, Management implications as the correlative survey suggests, and if so, what is the mechanism (changing root/shoot The scientific evidence from this project shows ratios, root extension, root hair development) clearly that sediment stability is a major factor in involved? determining recolonisation successand stability 3. What native British and/or Dutch species can of the recovering aquatic plant community. root firmly in fluid organic sediments, and how Macrophytes that recolonise in lakes with loose, is their rooting strength affected by sediment highly organic sediments are very susceptible to nutrients through root/shoot ratios, root physical disturbance from water flow or grazing. extension, root hair development? The 1995 They are easily dislodged from the sediment and survey did not give a coherent answer to this consequently will be lost from the aquatic question. community. This results in functionally annual 4. What is the role of the benthic filamentous behaviour. Macrophytes recolonising in firm algal layers as rooting substrates for colonising sediment lakes are firmly rooted and mainly submerged macrophytes after biomanipulation? perennial in behaviour. Physical disturbance will 35 4 I I S04-w K-s Na-w Eca..na 2 Enutt.. .•rci... co "U.•... 0 •.0... o I rd'Y" ~~':_~ ~p8~t o, Mvert ::J .. 1./'\ O'l .O'l- Q) ..L:•... '+- 0 -2 V\ Vic-, Pluce co .. 1Q3-w c " Redox-s co , Pobtu / r-. IV) , 80 1 70~ T / 1 'I 1 60~ / / I~ 1 I Sediment / 50J /1n I vi ~ +' ~ --.- Alderfen ~ U 40~ E ~ "tJ 0 Q) l.(') I i : 0\ I c Q) •.•• 30~ 1 - ~ -Fertilised sand Qj S }Jtrf ,;71 ~ U "tJ "-'" <;t ..s:::: 20~ j J c -+-' //tf~ty 1 I o on --11- - Ormesby c ~ e~ ...... Q) • I I/'~ I Cl -+-' 10 - 0 I ~ ..s: 0::: Q) rJ) 01 I T- -Pound end E 1 1 1 1 1 1 1 1 1 1 1 1 Q) N; 4040 4040 4040 3940 8 5 33386 7 2028 1725 81017231113915 810 \:) \.) 0 3 6 9 10 14 17 20 21 24 27 30 '+o- .c +' ra Cl r-- c ••••• Q) day after start experiment ••ClJ .. +'0 .-~. 0c u.. VI 0'\ M 600~1------~ 500 • I Sediment 400 I III +-' ~ ~ ~ 1 ---.- Alderfen E U 300 -u 0 ~ 0 . +-' If) 1 ~ 0\ Qj "' - ~ -Fertilised sand ;: S 200 -u U '<:t "-'" C ...s:::= o ~ I C bl) 3= ~ T --. --Ormesby 100 0'e1 ... ~--4 v, ~ .L 'Vi 0 J ~_~"!-}t- •• I ~ 0 ~ ...s:::= At ~ ~e.; ~ ~_~ -_.C_--I ~ rJ') O T--Pound end I [ e N = 40 40 3940 5 I 3940 40 40 4038 3940 2827 2930 2930 14 16 292914 IS 2020 1010 99 9 10 l.I..i '+o- o 3 5 6 9 10 14 17 20 21 24 27 30 35 41 ..c m +-' 00 ~ ••••• Q) C1J ~ day after start experiment '- 0 ~ 0 .~ ..c u, Vl .. 200------.------ vi +-' C o Q) E "U Q) In +-' C I •Q).. Q) 150 ~ "U o:;t o C o c o 3:: •o.. en o~- 100 VIc Q) -0 ---- C1:l on c '-' o o (S 0) u.i C) o Sediment '+o- .c ~a +-' o • en m o Pound end c 50 Q) m o 0) • +-' "- • o ~ o o o •Ormesby •.. ~ o o o o 0 a +-' o "U ~ • I 0 Fertilised sand Q) +-' •• • • rtl •Q).. ~ o •••.•• '1.. r r • -.-- r __ --,--- _ • Alderfen Q) u 20 40 60 80 100 C o 120 rtl +In-' In ..c• •Q).. Root length in sediment (cm) en .•...00 c QJ 0';; ••• 0 :::::s 0 C'I •.• •- Q. u.. :::> o o:;t <:t..- 60~,------· 50 Sediment 40 vi +-' C IJ 1 Q) E ",-..... ~ /1 ----.- Alderfen "'C / Q) U 30 +'"-' C Q) ~ •... l£) 1 Q) 1/. ; 0\ 1/ If "'C '" - • -Fertilised sand <:t S 20 /) C U 0 '-' c ~ J :;:: ~ 1 •0... --.--Ormesby Cl gf 10 .~- Q) .b ..- VI ~ .2 0 (1J I Q 0 ~ N rJ:J o T- -Pound end '+- 0 N= 3030 4040 3734 3030 16252627 1518 1314 1218 1314813 1214 9 10 .c +-' ca Cl 5 6 9 10 14 17 20 21 24 27 35 0'\ c •.... Q) Q) •... +-' ::::J 0 .-C\. 0c LL. VI day after start experiment '7 " Figure 19b. 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