Invertebrate footprints on detritus processing, bacterial community structure, and spatiotemporal redox profiles

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A house of cards: Patterns of aquatic invertebrate diversity in agricultural ditches

This thesis provides an overview of the interrelationships between different fractions of the ecosystem in North Holland’s intensively managed agricultural drainage ditches. It has been demonstrated that both submerged and emergent vegetation strongly influence invertebrate assemblages. Moreover, specific abiotic factors driving invertebrate diversity in these waters are associated with the inlet of mineral rich, river derived water and include concentrations of nutrients, bicarbonates and sulphate. Nutrients and macro-ions cause degradation of peat soils, leading to the accumulation of amorphous layers of mud in remnant peatland environments. In addition, temporal abiotic variability is structuring macroinvertebrate taxonomic and functional composition in the landscape. Agricultural intensification is placing increased pressures on aquatic ecosystems, via inputs of nutrients, suspended sediments and water abstraction. In the province of North Holland the demand for water is leading to greater influence of mineral rich waters which is ultimately degrading the aquatic environment. Moreover, the annual removal of vegetation is weakening the plant community which is already stressed by eutrophication and turbidity and this has a knock-on effect in causing a decline in invertebrate diversity. Despite the implementation of habitat improvement schemes, such as nature friendly banks in the Netherlands, there appears to be a lack of evidence supporting their effectiveness in promoting biodiversity. The isolation and size of these habitat creation measures are likely to be partially responsible. Small patches of suitable habitat, surrounded by a matrix of intensively managed agricultural land limit the ability of species to colonize these isolated habitats. For management strategies to successfully increase biodiversity in agricultural landscapes the requirements of habitat size and quality for biota must be met. Fortunately, with the large number of ditches and canals in North Holland’s landscape there is good potential to provide the habitat necessary to support a diverse range of aquatic biota, granted management seeks to do so

Temporal abiotic variability structures invertebrate communities in agricultural drainage ditches

Abiotic variability is known to structure lotic invertebrate communities, yet its influence on lentic invertebrates is not clear. This study tests the hypothesis that variability of nutrients and macro-ions are structuring invertebrate communities in agricultural drainage ditches. This was determined by investigating invertebrate adaptations to disturbance using insect life-history strategies. Many low-lying agricultural areas contain drainage ditches which potentially provide suitable habitat for aquatic invertebrates. In the province of North Holland (The Netherlands) the extensive network of eutrophic ditches are hydrologically managed, creating seasonal variability of water quality arising from agricultural run-off and the inlet of mineral rich, river derived water. This temporal variability was analysed from monitoring data, collected over a 7 month period (February till August) and covering 84 ditches in three soil regions; sand, clay and peat. Invertebrate diversity was determined as local (α diversity), regional (γ diversity) and species-turnover (β diversity). We ran canonical correspondence analysis and linear mixed models to determine correlations between invertebrate diversity, functional community composition and specific abiotic parameters, including variability (expressed as the Median Absolute Deviation). Invertebrate α diversity was positively correlated to variability in water transparency and negatively correlated to average pH, with the two parameters reflecting a water quality gradient in the environment. Insect life-history strategies expressed adaptations to abiotic variability and harsh (eutrophic) conditions. These adaptations were mainly achieved through good dispersal abilities and developmental trade-offs. The results support measures to reduce influxes of excess nutrients to this network of ditches

The role of emergent vegetation in structuring aquatic insect communities in peatland drainage ditches

Availability of macrophyte habitat is recognized as an important driver of aquatic insect communities in peatland drainage ditches; however, eutrophication can lead to the decline of submerged vegetation. While emergent vegetation is able to persist in eutrophicated ditches, vegetation removal, carried out during ditch maintenance, can reduce the availability of this habitat. In this study, we applied the landscape filtering approach to determine whether the absence of emergent vegetation is a habitat filter which structures aquatic insect communities in peatland drainage ditches under different trophic conditions. To this end, a field study was carried out in one mesotrophic (Naardermeer) and one eutrophic (Wormer and Jisperveld) peatland in the province of North Holland, The Netherlands. We assigned life history strategies to insect species and applied linear mixed models and redundancy analyses to taxonomic and functional aquatic insect community data. Our results indicate that while differences between peatlands primarily determine the species pool within each wetland, emergent vegetation acted as a secondary filter by structuring functional community composition within ditches. The eutrophic peatland was dominated by insects adapted to abiotic extremes, while species with good dispersal abilities were strongly related to emergent vegetation cover. This study demonstrates the applicability of life history strategies to provide insight into the filtering of species due to availability of emergent macrophyte habitat. To ensure greater diversity of insect communities in ditch habitats, it is recommended that some vegetation be spared during maintenance to leave patches from which insect recolonization can occur

Linkages between benthic microbial and feshwater insect communities in degraded peatland ditches

Many wetlands are heavily modified and identifying the environmental drivers of indicator groups like aquatic insects is complicated by multiple stressors and co-varying environmental factors. Yet, incorporating data from other biological groups, such as microbial communities, potentially reveals which environmental factors are underpinning insect community composition. In the present study we investigated the application of benthic microbial community composition, as determined by phospholipid fatty acid (PLFA) analysis, alongside aquatic insect data in 25 peatland ditches in the province of North Holland, The Netherlands. We applied clustering and principal component analysis to a matrix of 26 PLFAs to group ditches by the microbial community. Generalized linear models were used to examine correlations between microbial PLFAs, insects, vegetation (emergent and submerged) and abiotic factors. The ratio of heterotrophic (e.g. sulphate reducing bacteria) to autotrophic (e.g. algae and cyanobacteria) derived PLFAs could be estimated as the ratio between saturated and branched to monounsaturated and polyunsaturated fatty acids (SB/MP). SB/MP was correlated with insect community composition, differences in water chemistry (in particular bicarbonate, sulphate and nutrients) and vegetation cover in the ditches. Moreover, ditches distinguished by their microbial communities differed in the number of insects they supported with differences most pronounced for Odonata, Trichoptera and Chironomus larvae. This study demonstrates that integrating microbial and aquatic insect community data provides insight into key environmental drivers in modified aquatic ecosystems and may facilitate the development of remediation strategies for degraded wetlands