2c: Connected by water

2c: Connected by water

Conveners:       Arie Vonk, University of Amsterdam

                        Casper van Leeuwen, Radboud University

1. The role of anecic earthworm Lumbricus terrestris in improving water regulation on grasslands 

Roos van de Logt, Louis Bolk Institute

Water regulation is an important non-provisional ecosystem service of grasslands, especially under the current trend of increasing peak rains and droughts. Anecic earthworm Lumbricus terrestris can contribute to this. This ecosystem engineer creates semi-permanent vertical burrows with a depth of up to 2m, which increase the soil’s water infiltration rate and capacity, while facilitating plant root penetration into deeper layers, thus increasing drought resistance. Inoculation of grasslands with L. terrestris (native species to temperate Europe) could be an ecological innovation to improve water regulation. We executed a mesocosm experiment at dairy farms to explore the ability of L. terrestris to survive and reproduce after inoculation. Results showed that L. terrestris was able to survive, burrow >60 cm and produce offspring. However survival rate was modest (15-26%). Long-term experiments in non-enclosed plots and a better understanding of potential pathogen-pressure are needed to validate the feasibility of L. terrestris inoculation in practice.   

2. Long-term development of phytoplankton community in a highly modified coastal lake: Markermeer, the Netherlands

Laura Tack, Arie Vonk, Jef Huisman, Jolanda Verspagen, Harm van der Geest, Universiteit van Amsterdam / Rijkswaterstaat

 Demands for water safety, freshwater supply as well as land reclamation can drive huge hydromorphological impacts on shallow coastal bay areas and lead to fragmented, compartmentalized coastal lake systems. In these highly modified systems hydrological regimes are artificially altered and nutrient cycling impacted, leading to changes in nutrient concentrations as well as stoichiometry. To investigate how these changes in nutrient concentrations and stoichiometry can impact ecological functioning and specifically phytoplankton dynamics we investigate phytoplankton abundance and community composition. We hereby look at long time series data starting in roughly 1976 when due to the construction of the Houtribdijk the large and shallow coastal lake Markermeer (NL) was isolated until now (2022). By doing so we try to unravel the effects of such hydromorphological changes on coastal lake ecosystems and potential bottlenecks as well as ways forward to ecosystem restoration.

3. Spatial proxies in machine learning models – when cross validation fails to catch overfitting 

Herman de Munnik, Utrecht University  

Sea-level rise necessitates the implementation of flood-risk management strategies, and closing estuaries is part of the consideration. Consequently, environmental predictions on the impact of seawalls are becoming increasingly important. One method to assess their environmental impact involves training models on closed estuaries and extrapolating the results to open estuaries. Random Forest (RF) models are a popular choice in environmental science when prediction accuracy is of primary concern. However, extrapolating spatially explicit RF models beyond the spatial range of the training data can cause prediction errors; especially when training data are clustered. To make matters worse, spatially explicit RF models often performs better in terms of minimising loss-functions; across most common cross validation techniques. In this study, I highlight the problems that arise when extrapolating a RF, trained on clustered data, beyond the spatial range of the training data. Data from Lake Grevelingen are used to train the model, and extrapolated to the Eastern Scheldt.   

4. Duck Tales: Spatio-temporal dynamics of habitat use and prey relationships of Common Eider and its implication for conservation management 

Kasper J. Meijer, Oscar Franken, Allert Bijleveld, Mennobart van Eerden, Tjisse van der Heide, Laura L. Govers, Han Olff, Groningen Institute for Evolutionary Life Sciences  

Effective protection of endangered and vulnerable species requires an in-depth understanding of spatiotemporal patterns relating to resource use and human threats. This is extra challenging for mobile species, like the common eider (Somateria mollisima). The eider is an important target species for the North Sea region, one of its major wintering sites. However, in many wintering sites, no area-specific measures are in place regarding this species. Here, we use long-term (1993-2023) monitoring data to identify spatiotemporally predictable hotspots of wintering eiders. We find clear hotspots of wintering eiders, which correspond to places with high abundances of their preferred prey. However, the current spatial layout of protection measures poorly overlaps with these hotspots. This mismatch emphasizes the need to better align conservation goals and practices. Explicit knowledge of spatiotemporal resource use can aid in designing Marine Protected Areas with clear objectives and boundaries. 

5. Identifying habitat preferences of two co-occurring and morphological similar sandeel species in the southern North Sea 

Bram Parmentier, Royal Netherlands Institute for Sea Research  

Sandeel plays a central role in marine food webs as a prey for top predators, including seabirds, marine mammals, and piscivorous fish. Despite their importance, reliable quantitative data on these small fish are limited due to their burrowing behavior and slender body, which are challenging for conventual survey methods. Along the Dutch coast, two morphologically similar species, small sandeel (Ammodytes tobianus) and lesser sandeel (Ammodytes marinus), coexist. By integrating data from the WOT shellfish survey and NIOZ Triple-D dredge, we constructed spatial distribution maps to uncover species-specific habitat preferences. These insights help clarify the distinct ecological roles of these species within the marine food web of the southern North Sea.