Macrophyte loss drives decadal change in benthic invertebrates in peatland drainage ditches

Abstract

Summary Agricultural peatlands and their associated drainage systems are often highly managed and exposed to anthropogenic pressures, such as eutrophication and stable water tables, maintained via drainage during periods of high rainfall and inlet of, alkaline‐rich, waters during dry periods. These pressures promote peat degradation, resulting in the accumulation of fine‐degraded peat particles that dramatically alter aquatic habitats by smothering surfaces and decreasing water quality. Consequential effects on benthic communities are expected but have not been investigated so far. We hypothesised that peat degradation can lead to the decline in submerged macrophytes, which are of critical importance to sustaining biodiversity of benthic invertebrate communities. To investigate this, we analysed decadal (1985–2007) changes in benthic species richness in 29 peat ditches in the Netherlands and, to determine patterns of macroinvertebrate habitat occupancy, carried out a complementary field experiment with submerged artificial macrophytes, natural sediments and emergent bank vegetation. Results from long‐term monitoring indicate that chemical conditions in agricultural peat ditches have improved slightly over the last decades; however, there has been a simultaneous decline in benthic invertebrate species richness and densities corresponding to a decline in the numbers of submerged macrophytes. The apparent dependence of macroinvertebrates on macrophytes was reinforced by our field experiment which revealed that invertebrate density was highest in submerged artificial plants, while invertebrate species richness was highest in natural emergent vegetation. Conversely, degraded peat sediments supported extremely few invertebrates. Our results clearly illustrate the strong influence of submerged macrophyte loss on macroinvertebrate assemblages in peatland waters. Furthermore, this suggests that improvements in water quality alone will not benefit invertebrates in the absence of suitable vegetative habitats.

Disentangling food webs interactions in the littoral of temperate shallow lakes

“…stands, thus increase the diversity of benthic macroinvertebrates among the macrophyte stems. On the other hand, the substantial decline in macroinvertebrate diversity corresponded significantly to a reduction in the structural heterogeneity in the water bodies; this is similar to the results of studies on Lago di Candia, northern Italy (Cremona et al, 2008) and peat ditches in the Netherlands (Whatley et al, 2014). Rotifers and ciliates, which comprised a considerable proportion of the plankton and epiphyton diversity, did not differ significantly among the studied water bodies.…”

Aquatic macroinvertebrate biodiversity associated with artificial agricultural drainage ditches

“…The management practices, primarily designed to maintain the hydrological functioning (conveyance of water) may actually inadvertently promote and enhance aquatic macroinvertebrate diversity. Ditch cleaning Fairly high, high and very high conservation value scores are presented in bold and dredging has been shown to positively influence Trichoptera presence in ditches (Twisk et al, 2000), and dredging can remove nutrient-rich sediment (Whatley et al, 2014a) and reset ditch habitats to an earlier successional stages (Clarke, 2015). The rotational management of sites over time means a variety of vegetation successional stages will be present across the sites and collectively these provide a wide range of habitats suitable for macroinvertebrates (Painter et al, 1999;Clarke, 2015).…”

Combined impact of pesticides and other environmental stressors on taxonomic richness of freshwater animals in irrigation ponds

“…Some of the studied ponds had high concentrations of two herbicides, butachlor and pentoxazone (S2 Fig), which were far higher than their acute toxicity levels for the ecotoxicological bioindicator Raphidocelis subcapitata (72-h ErC50, 3.15 μg/L [33] and 0.79 μg/L [34], respectively). The decline of macrophytes can drive decadal change in benthic invertebrates [35]. To clarify this viewpoint, we transformed the percentages of floating-leaved plant coverage and emergent plant coverage into the area percentages not covered by these types of plants, as follows: 100 – (floating-leaved plant coverage) and 100 – (emergent plant coverage), respectively.…”