Broad-scale patterns of invertebrate richness and community composition in temporary rivers: effects of flow intermittence

Temporary rivers are increasingly common freshwater ecosystems, but there have been no global syntheses of their community patterns. In this study, we examined the responses of aquatic invertebrate communities to flow intermittence in 14 rivers from multiple biogeographic regions covering a wide range of flow intermittence and spatial arrangements of perennial and temporary reaches. Hydrological data were used to describe flow intermittence (FI, the proportion of the year without surface water) gradients. Linear mixed-effects models were used to examine the relationships between FI and community structure and composition. We also tested if communities at the most temporary sites were nested subsets of communities at the least temporary and perennial sites. Taxon richness decreased as FI increased and invertebrate communities became dominated by ubiquitous taxa. The number of resilient taxa (with high dispersal capacities) decreased with increased FI, whereas the number of resistant taxa (with adaptations to desiccation) was not related to FI. River-specific and river-averaged model comparisons indicated most FI-community relationships did not differ statistically among rivers. Community nestedness along FI gradients was detected in most rivers and there was little or no influence of the spatial arrangement of perennial and temporary reaches. These results indicate that FI is a primary driver of aquatic communities in temporary rivers, regardless of the biogeographic species pool. Community responses are largely due to resilience rather than resistance mechanisms. However, contrary to our expectations, resilience was not strongly influenced by spatial fragmentation patterns, suggesting that colonist sources other than adjacent perennial reaches were important. © 2013 The Authors

Rock snot and lake mud: exploring the history of recent blooms of didymosphenia geminata using information contained in lake sediments

Ecosystem managers have often considered the nuisance diatom species, Didymosphenia gemi¬nata (didymo) as being introduced to the natural environment through human activities; however, observations from early 20th-century surveys challenge this characterization. We use diatoms pre¬served in lake sediment cores to investigate the history of didymo blooms from Gaspésie, Quebec. Relative abundances of diatoms were examined from the dated sediments of Lac Humqui and Lac au Saumon (a lake with an inflowing river currently supporting blooms). Didymo was observed throughout the Lac au Saumon core, demonstrating that it has been present in the region well before the first reports of blooms in 2006. Lac Humqui diatom assemblages experienced a shift in composition with declines in benthic taxa (attached to substrates) and increases in planktonic (free floating) diatoms that began ~1970. Strong relationships between this diatom shift, and increases in regional air temperatures and earlier river ice-out dates were consistent with the expected effects of climate warming on aquatic systems. Our paleolimnological evidence shows that climate warming, rather than human introduction, likely plays an important role in triggering didymo blooms

New Zealand freshwater management and agricultural impacts

In New Zealand, it is increasingly recognised, including by government, that water resource allocation and water quality are issues of national importance. Agriculture is frequently portrayed by public media as a major user of water and a major contributor to worsening water quality. We outline the water management systems in New Zealand, and the use of water by agriculture. Official reports on agriculture's impact on New Zealand water availability and quality are summarised. We report how the New Zealand public perceive water, its management, and the roles of agriculture in water issues. Data from a nationwide mail survey were analysed to determine how New Zealanders assess the state of New Zealand lakes, rivers and streams, and aquifers, the performance of three agencies responsible for management of freshwater resources, and willingness to fund stream enhancement. We provide brief explanations for the failures of water resource management in New Zealand and report on options, including community-based responses that might address some of the mounting public, scientific, and government concerns about trends in water quantity and quality. A willingness to pay proposition, concerning riparian areas, included in the nationwide survey provides some evidence that the public are willing to pay for improved waterway management. Relevant non-market valuation studies also indicate that the public places considerable value on preservation values of water in New Zealand. Copyright Australian Agricultural and Resource Economics Society Inc. and Blackwell Publishing Ltd 2006.