|De werking van RWS KRW maatregelen in conceptuele relatieschema's
Geerling, G.J. ; Buijse, A.D. ; Liefveld, Wendy ; Katwijk, M.M. van; Groot, A.V. de - \ 2016
Deltares - 42 p.
KRW - Natura 2000 - rijkswateren - herstelmaatregelen - relatieschema - conceptueel schema
Positive feedbacks in seagrass ecosystems - evidence from large-scale empirical data
Heide, Tj. van; Nes, E.H. van; Katwijk, M.M. van; Olff, H. ; Smolders, A.J.P. - \ 2011
PLoS ONE 6 (2011)1. - ISSN 1932-6203 - 7 p.
eelgrass zostera-marina - posidonia-oceanica - toxicity - nitrogen - meadow - shifts - water - beds - flow
Positive feedbacks cause a nonlinear response of ecosystems to environmental change and may even cause bistability. Even though the importance of feedback mechanisms has been demonstrated for many types of ecosystems, their identification and quantification is still difficult. Here, we investigated whether positive feedbacks between seagrasses and light conditions are likely in seagrass ecosystems dominated by the temperate seagrass Zostera marina. We applied a combination of multiple linear regression and structural equation modeling (SEM) on a dataset containing 83 sites scattered across Western Europe. Results confirmed that a positive feedback between sediment conditions, light conditions and seagrass density is likely to exist in seagrass ecosystems. This feedback indicated that seagrasses are able to trap and stabilize suspended sediments, which in turn improves water clarity and seagrass growth conditions. Furthermore, our analyses demonstrated that effects of eutrophication on light conditions, as indicated by surface water total nitrogen, were on average at least as important as sediment conditions. This suggests that in general, eutrophication might be the most important factor controlling seagrasses in sheltered estuaries, while the seagrass-sediment-light feedback is a dominant mechanism in more exposed areas. Our study demonstrates the potentials of SEM to identify and quantify positive feedbacks mechanisms for ecosystems and other complex systems
Alternative Stable States Driven by Density-Dependent Toxicity
Heide, T. van der; Nes, E.H. van; Katwijk, M.M. van; Scheffer, M. ; Hendriks, A.J. ; Smolders, A.J.P. - \ 2010
Ecosystems 13 (2010)6. - ISSN 1432-9840 - p. 841 - 850.
eelgrass zostera-marina - distinguishing resource competition - fresh-water wetlands - vegetation dieback - baltic sea - ecosystems - sulfide - phytotoxicity - interference - populations
Many populations are exposed to naturally occurring or synthetic toxicants. An increasing number of studies demonstrate that the toxicity of such compounds is not only dependent on the concentration or load, but also on the biomass or density of exposed organisms. At high biomass, organisms may be able to alleviate adverse effects of the toxicant by actively lowering ambient concentrations through either a joint detoxification mechanism or growth dilution. We show in a conceptual model that this mechanism may potentially lead to alternative stable states if the toxicant is lethal at low densities of organisms, whereas a high density is able to reduce the toxicant concentrations to sub-lethal levels. We show in an example that this effect may be relevant in real ecosystems. In an earlier published experimental laboratory study, we demonstrated that ammonia toxicity in eelgrass is highly dependent on the eelgrass shoot density. Here, we used the results of these experiments to construct a model describing the complex interactions between the temperate seagrass Zostera marina and potentially lethal ammonia. Analyses of the model show that alternative stable states are indeed present over wide ranges of key-parameter settings, suggesting that the mechanism might be important especially in sheltered, eutrophicated estuaries where mixing of the water layer is poor. We argue that the same mechanism could cause alternative stable states in other biological systems as well.
Predicting habitat suitability in temperate seagrass ecosystems
Heide, Tj. van; Peeters, E.T.H.M. ; Hermus, D.C.R. ; Katwijk, M.M. van; Roelofs, J.G.M. ; Smolders, A.J.P. - \ 2009
Limnology and Oceanography 54 (2009)6. - ISSN 0024-3590 - p. 2018 - 2024.
eelgrass zostera-marina - water - eutrophication - restoration - toxicity - nitrogen - growth - sea
The worldwide observed dramatic decline of seagrasses has typically been attributed to multiple stressors such as eutrophication, disease, sedimentation, and toxicity events. Using principal component analysis and (multivariate) logistic regression, we investigated the importance of 30 commonly measured variables in explaining the presence and absence of the temperate seagrass species Zostera marina and Zostera noltii at 84 Western European locations. Although many interrelated variables influence seagrass presence in our dataset, presence or absence of both species could be reliably predicted by using only two easy-to-measure variables. A logistic regression model of Z. marina correctly predicted 77% of all observations by including water column light attenuation and sediment pore-water reduction oxidation potential (RedOx). The Z. noltii model had an 86% accuracy based on only tidal location (intertidal or subtidal zone) and pore-water RedOx. Applying the models to five evaluation sites demonstrated that both models can be usefully applied as tools for seagrass ecosystem restoration and conservation
Toxicity of reduced nitrogen in eelgrass (Zostera marina) is highly dependent on shoot density and pH
Heide, Tj. van; Smolders, A.J.P. ; Rijkens, B. ; Nes, E.H. van; Katwijk, M.M. van; Roelofs, J.G.M. - \ 2008
Oecologia 158 (2008)3. - ISSN 0029-8549 - p. 411 - 419.
free amino-acids - water-column nitrate - false discovery rate - ammonium toxicity - submersed macrophyte - seagrass ecosystems - nutritional-status - sediment sulfide - nh4+ toxicity - pine needles
In sheltered, eutrophicated estuaries, reduced nitrogen (NH x ), and pH levels in the water layer can be greatly enhanced. In laboratory experiments, we studied the interactive effects of NH x , pH, and shoot density on the physiology and survival of eelgrass (Zostera marina). We tested long-term tolerance to NH x at pH 8 in a 5-week experiment. Short-term tolerance was tested for two shoot densities at both pH 8 and 9 in a 5-day experiment. At pH 8, eelgrass accumulated nitrogen as free amino acids when exposed to high loads of NH x , but showed no signs of necrosis. Low shoot density treatments became necrotic within days when exposed to NH x at pH 9. Increased NH3 intrusion and carbon limitation seemed to be the cause of this, as intracellular NH x could no longer be assimilated. Remarkably, experiments with high shoot densities at pH 9 showed hardly any necrosis, as the plants seemed to be able to alleviate the toxic effects of high NH x loads through joint NH x uptake. Our results suggest that NH x toxicity can be important in worldwide observed seagrass mass mortalities. We argue that the mitigating effect of high seagrass biomass on NH x toxicity is a positive feedback mechanism, potentially leading to alternative stable states in field conditions.
Positive feedbacks in seagrass ecosystems - implications for success in conservation and restoration
Heide, Tj. van; Nes, E.H. van; Geerling, G.W. ; Smolders, A.J.P. ; Bouma, T.J. ; Katwijk, M.M. van - \ 2007
Ecosystems 10 (2007)8. - ISSN 1432-9840 - p. 1311 - 1322.
dutch wadden-sea - eelgrass zostera-marina - catastrophic regime shifts - shallow lakes - dynamics - beds - attenuation - meadow - growth - wind
Seagrasses are threatened by human activity in many locations around the world. Their decline is often characterized by sudden ecosystem collapse from a vegetated to a bare state. In the 1930s, such a dramatic event happened in the Dutch Wadden Sea. Before the shift, large seagrass beds (Zostera marina) were present in this area. After the construction of a large dam and an incidence of the ¿wasting disease¿ in the early 1930s, these meadows became virtually extinct and never recovered despite restoration attempts. We investigated whether this shift could be explained as a critical transition between alternative stable states, and whether the lack of recovery could be due to the high resilience of the new turbid state. We analyzed the depth distribution of the historical meadows, a long-term dataset of key factors determining turbidity and a minimal model based on these data. Results demonstrate that recovery was impossible because turbidity related to suspended sediment was too high, probably because turbidity was no longer reduced by seagrass itself. Model simulations on the positive feedback suggest indeed the robust occurrence of alternative stable states and a high resilience of the current turbid state. As positive feedbacks are common in seagrasses, our findings may explain both the worldwide observed collapses and the low success rate of restoration attempts of seagrass habitats. Therefore, appreciation of ecosystem resilience may be crucial in seagrass ecosystem management.
Kansenkaart zeegras Waddenzee : potentiële groeimogelijkheden voor zeegras in de Waddenzee
Jong, D.J. de; Katwijk, M.M. van; Brinkman, A.G. - \ 2005
S.l. : RIKZ (Rapport RIKZ 2005.013) - 51
zostera - groei - habitats - ecologie - plant introduction - milieufactoren - nederland - waddenzee - zostera - growth - habitats - ecology - plant introduction - environmental factors - netherlands - wadden sea
|Eelgrass (Zostera marina L.) in the western Wadden Sea: monitoring, habitat suitability model, transplantations and communication
Bos, A.R. ; Dankers, N.M.J.A. ; Groeneweg, A.H. ; Hermus, D.C.R. ; Jager, Z. ; Jong, D.J. de; Smit, T. ; Vlas, J. de; Wieringen, M. van; Katwijk, M.M. van - \ 2005
In: Proceedings Dunes and Estuaries 2005; VIZ Special Publication 19. - Oostende (Belgium) : VLIZ - p. 95 - 109.
Handleiding voor het gebruik van multivariate analysetechnieken in de ecologie
Katwijk, M.M. van; Braak, C.J.F. ter - \ 2003
Wageningen : PRI Biometris - 36 p.