Insecticides and Drought as a Fatal Combination for a Stream Macroinvertebrate Assemblage in a Catchment Area Exploited by Large-Scale Agriculture

This case study documents responses in a headwater macroinvertebrate assemblage to insecticide pollution and hydrological drought. In 2014, the Doubravka brook (Czech Republic) was damaged by a large overflow of a mixture of chlorpyrifos (CPS) and cypermethrin (CP). In 2016–2017, this brook was then affected by severe drought that sometimes led to an almost complete absence of surface water. We found significant relationships between the strength of both these disturbances and the deeper taxonomic levels of both the overall macroinvertebrate assemblage (classes) and the arthropod assemblage alone (orders and dipteran families), as well as the functional feeding groups (FFGs). The CPS-CP contamination was mostly negatively correlated to arthropod and non-arthropod taxa and was positively correlated only with FFG collector-gatherers; on the other hand, the drought was negatively correlated to Simuliidae, Ephemeroptera, Trichoptera, and the FFG of grazer-scrapers and passive filterers. Drought conditions correlated most positively with Isopoda, Ostracoda, Heteroptera, adult Coleoptera, and predator and active filterer FFGs. The chosen eco-indicators (SPEARpesticides, SPEARrefuge, BMWP, and EPT) used as support information reveal the poor ecological status of the whole assemblage, including the control site, the cause of which is most likely to be the exploitation of the adjacent catchment area by large-scale agriculture. This type of agricultural exploitation will undoubtedly affect macroinvertebrate assemblages as a result of agrochemical and soil inputs during run-off events and will also exacerbate the effect of droughts when precipitation levels drop.

Biochemical influence of amphidromous shrimps on stream ecosystems in Japan

Not only through species interactions but also through excretion of nutrients, consumers can have profound effects on the ecosystem structure. While many studies in lentic ecosystems address both effects in combination, little is known about their linkages in lotic ecosystems. By a combination of field manipulative experiment, excretion measurements of consumes, and field surveys, we evaluated biochemical effects of amphidromous shrimps on stream ecosystems. The field manipulative experiment showed that the presence of shrimp suppressed the total aquatic insect biomass by 9% but increased the total benthic macroinvertebrate biomass including the shrimps by 196%. The biomass-specific NH4+ excretion rate by shrimp was similar to aquatic insects, and the calculated mean NH4+ excretion by benthic macroinvertebrate assemblage was 144% higher in the presence of shrimps. On the other hand, shrimps excreted much less PO43− than aquatic insects, and the PO43− excretion by the benthic macroinvertebrate assemblage did not change by the presence of shrimps. The field survey showed a positive correlation between NO3− concentration in stream water and shrimp density, suggesting that the excess NH4+ was nitrified and raised NO3− concentration. In contrast, PO43− concentration in stream water was negatively associated with the shrimp density, indicating that the dominance of shrimps that excrete little PO43− decreased the PO43− concentration. While nutrient concentration of stream water is often attributed to the condition of the watershed area, the results of this study indicate downstream connectivity to the ocean can also influence the nutrient dynamics of the stream through the density of amphidromous shrimps.

Unique habitat and macroinvertebrate assemblage structures in spring-fed streams: a comparison among lowland tributaries and mainstreams in northern Japan

The stable flow and temperature regimes of spring-fed streams are distinct from the dynamic regimes of other streams. We investigated differences in habitat and macroinvertebrate assemblages among a spring-fed tributary, an adjacent non-spring-fed tributary, and mainstream reaches. Current velocity was slowest in the spring-fed reach and percent fine sediment deposition was 3.8–13.9 times higher than in non-spring streams. Mean periphyton biomass was greatest in the mainstream reach where canopy openness was greatest, whereas the standing stock of detritus was greatest in the spring-fed reach. These results suggest that the stable flow regime in the spring-fed stream leads to the accumulation of fine sediment and detritus on the streambed. Oligochaeta and chironomids, which are burrower-gatherers, were remarkably abundant in the spring-fed reach and total macroinvertebrate abundance was 3.4–12.2 times greater than in the other reaches. Sprawler-grazer ephemeropterans were abundant in the mainstream reaches, likely due to higher primary productivity. Allomyia sp, which depend on cool spring-fed habitats, were found only in the spring-fed reach. The macroinvertebrate assemblage in the spring-fed reach was characterized by numerous burrowers, collector-gatherers, and crenobiont taxa, highlighting the contribution of these habitats to beta diversity in river networks.

Coastal Wetlands: Ecosystems Affected by Urbanization?

Coastal wetlands are ecosystems that provide multiple benefits to human settlements; nonetheless, they are seriously threatened due to both a lack of planning instruments and human activities associated mainly with urban growth. An understanding of their functioning and status is crucial for their protection and conservation. Two wetlands with different degrees of urbanization, Rocuant-Andalién (highly urbanized) and Tubul-Raqui (with little urbanization), were analyzed using temperature, salinity, dissolved oxygen, pH, turbidity, granulometry, fecal coliform, and macroinvertebrate assemblage variables in summer and winter. In both wetlands marked seasonality in salinity, temperature and sediment texture classification, regulated by oceanic influence and changes in the freshwater budget, was observed. In the Rocuant-Andalién wetland, the increases in pH, dissolved oxygen, gravel percentage, and coliform concentration were statistically significant. Urbanization generated negative impacts on macroinvertebrate assemblage structure that inhabit the wetlands; greater richness and abundance (8.5 times greater) were recorded in the Tubul-Raqui wetland than in the more urbanized wetland. The multivariate statistical analysis reflects the alteration of these complex systems.