The impact of flooding on aquatic ecosystem services

Flooding is a major disturbance that impacts aquatic ecosystems and the ecosystem services that they provide. Predicted increases in global flood risk due to land use change and water cycle intensification will likely only increase the frequency and severity of these impacts. Extreme flooding events can cause loss of life and significant destruction to property and infrastructure, effects that are easily recognized and frequently reported in the media. However, flooding also has many other effects on people through freshwater aquatic ecosystem services, which often go unrecognized because they are less evident and can be difficult to evaluate. Here, we identify the effects that small magnitude frequently occurring floods ( 100-year recurrence interval) have on ten aquatic ecosystem services through a systematic literature review. We focused on ecosystem services considered by the Millennium Ecosystem Assessment including: (1) supporting services (primary production, soil formation), (2) regulating services (water regulation, water quality, disease regulation, climate regulation), (3) provisioning services (drinking water, food supply), and (4) cultural services (aesthetic value, recreation and tourism). The literature search resulted in 117 studies and each of the ten ecosystem services was represented by an average of 12 ± 4 studies. Extreme floods resulted in losses in almost every ecosystem service considered in this study. However, small floods had neutral or positive effects on half of the ecosystem services we considered. For example, small floods led to increases in primary production, water regulation, and recreation and tourism. Decision-making that preserves small floods while reducing the impacts of extreme floods can increase ecosystem service provision and minimize losses

Carbon and nitrogen flows through the benthic food web of a photic subtidal sandy sediment

Carbon and nitrogen flows within the food web of a subtidal sandy sediment were studied using stable isotope natural abundances and tracer addition. Natural abundances of 13C and 15N stable isotopes of the consumers and their potential benthic and pelagic resources were measured. δ13C data revealed that consumers did not feed on the bulk microphytobenthos (MPB) but rather were selective in their food uptake, preferring either benthic diatoms (–16‰), or benthic cyanobacteria (–20‰). MPB was labelled through a pulse-chase experiment with 13C-bicarbonate and 15N-nitrate. The fate of MPB was followed in the different heterotrophic compartments. Transfer of 13C and 15N to consumers was fast, although only a small fraction of total label was transferred to the heterotrophic compartments within the 4 d of the experiment. Heterotrophic bacteria were responsible for most of the total heterotrophic incorporation of 13C. Within the metazoan community, the incorporation of 13C by the meiofauna was more than 2-fold that of the macrofauna, despite a significantly lower biomass. The dual labelling also revealed differential feeding or assimilation strategies in meio- and macrofauna. The low 13C:15N ratios of the meiofauna (the smaller organisms) seemed to indicate that they preferentially assimilated N or specifically grazed on N-rich resources. However, the macrofauna (larger organisms) seemed to feed on bulk sediment, consistent with high 13C:15N ratios. This dual approach, which combined natural abundance and a pulse-chase addition of stable isotopes, revealed crucial information on the key role of MPB in structuring benthic communities in sandy sediments

Scenarios of freshwater fish extinctions from climate change and water withdrawal

Reductions in river discharge (water availability) like those from climate change or increased water withdrawal, reduce freshwater biodiversity. We combined two scenarios from the Intergovernmental Panel for Climate Change with a global hydrological model to build global scenarios of future losses in river discharge from climate change and increased water withdrawal. Applying these results to known relationships between fish species and discharge, we build scenarios of losses (at equilibrium) of riverine fish richness. In rivers with reduced discharge, up to 75% (quartile range 4-22%) of local fish biodiversity would be headed toward extinction by 2070 because of combined changes in climate and water consumption. Fish loss in the scenarios fell disproportionately on poor countries. Reductions in water consumption could prevent many of the extinctions in these scenarios. © 2005 Blackwell Publishing Ltd

Turbulence and stratification in Priest Pot, a productive pond in a sheltered environment.

Priest Pot is an example of the abundant ponds which, collectively, contribute crucially to species diversity. Despite extensive biological study, little has been reported about the physical framework which supports its ecological richness. This paper elucidates the physical character of Priest Pot�s water column and thus that of similar waterbodies. Vertical thermal microstructure profiles were recorded during summer 2003, and analysed alongside concurrent meteorological data. During summer stratification, the thermal structure appeared to be dominated by surface heat fluxes. Surface wind stress, limited by sheltering vegetation, caused turbulent overturns once a surface mixed layer was present, but appeared to contribute little to setting up the thermal structure. Variations in full-depth mean stratification occurred pre-dominantly over seasonal and ~5-day time scales, the passage of atmospheric pressure systems being posited as the cause of the latter. In the uppermost ~0.5 m, where the stratification varied at sub-daily time scales, turbulence was active (sensu Ivey and Imberger, 1991) when this layer was mixed, with dissipation values � ~ 10-8 m2s-3 and vertical diffusivity KZ = 10-4-10-6 m2s-1. Where the water column was stratified, turbulence was strongly damped by both buoyancy and viscosity and KZ was an order of magnitude smaller. Vertical transport in the mixed layer occurred via many small overturns (Thorpe scale rms and maximum values typically 0.02m and 0.10m respectively) and seston were fully mixed through the water column