They are a key component of the food chain and their abundance and diversity have been used to assess the ecosystem health and bio diversity in a given habitat.
A very recent study by Leroy et al iexamined the relative importance of litter quality and stream characteristics in determining decomposition rate and macro invertebrate assemblage living on autumn shed leaves. The decomposition rates of five riparian tree species (Populus fermonti, Alnus oblongifolnia, Platanus wrightii, Faxinus velutina, Quercus gambelli) were compared across three south -western streams in the Verde River catchments (Arizona, U.S.A). Also to test whether plant species diversity affects rate, the decomposition of three and five species mixtures was compared to that of a single species. The results showed that decomposition rate was affected by both litter quality and stream although litter quality accounted for most of the variation. The relative importance of litter quantity was shown to decrease from 97% in the first week to 45% by the eighth week. It was also found that the rate of decomposition increased relatively when all the species included were highly labile. The most significant outcome of this study was the difference in invertebrate assemblage, which seemed to be more pronounced across streams than across leaf litter species within a stream. There was also a significant difference between the invertebrate assemblage colonizing leaf mixtures compared to that colonizing pure species litter, indicating non -additive properties of litter diversity on stream invertebrates. The conclusion of the study was that leaf litter diversity has the capacity to affect in -stream decomposition rates and stream invertebrates but these effects depend on both litter quality and stream characteristics.
A research conducted in Griffith University, Australiaii studied the basic principles and ecological consequences of altered flow regimens for aquatic bio- diversity. The article stated that the flow regimen is considered to be the primary factor governing river and flood plain wetland ecosystems. Four key principles highlighted the important mechanisms that link hydrology and aquatic bio diversity and the impacts of alteration in the flow regimes:
1. Flow plays a major role in determining the physical habitat in streams, which influences the biotic composition.
2. The evolution of aquatic species has a direct response to the natural flow regimes.
3. The viability of populations of many riverine species requires maintenance of natural patterns of longitudinal and lateral connectivity.
4. The alteration in flow regimes facilitates the invasion and success of exotic and introduced species in riverine systems.
Wide ranges of taxonomic groups are impacted by altered flow regimes including riverine plants, invertebrates and fish.
A study by Douglas et al iii related macro invertebrate community structure to physical, chemical and biological gradients in flow through constructed wetlands receiving secondarily treated domestic wastewater and lower nutrient river water in Ohio, U.S.A. Benthic colonization plates and emergence traps were used to collect macro invertebrates which were then analyzed with diversity, biotic and combination indices and related to seventeen parameters of water quality, substrate characteristics and primary productivity in both wetland systems. 36 and 39 macro invertebrate