Assessing the fate and biodegradation of cyanobacterial metabolites in Australian waters

With the exception of the saxitoxins, the cyanobacterial metabolites studied were shown to be biodegradable in two South Australian waters with the rate of biodegradation of the metabolites influenced by temperature and to a lesser extent, seasonal variations. The order of ease of biodegradability followed the trend: microcystin-LR > cylindrospermopsin > geosmin > 2-methylisoborneol > saxitoxins. Pseudo-first-order rate constants for the biodegradation of the metabolites ranged from 9.6 × 10−4 to 2.6 × 10−2 h−1.Tim Tang, Daniel Hoefel, Thorsten Mosisch and Lionel H

Ecosystem measures of river health and their response to riparian and catchment degradation

1. Measurements of ecological patterns are often used as primary biological indicators of river health. However, these patterns provide little information about important stream ecosystem processes (e.g. the sources and fate of energy and nutrients). The direct measurement of these processes is considered fundamental to the determination of the health of stream and river ecosystems. 2. In this paper we used two basic approaches to assess stream ecosystem response to catchment disturbance and, particularly, to the loss of riparian vegetation in different forested biomes across Australia. Benthic gross primary production (GPP) and respiration (R24) provided measures of the amounts of organic carbon produced and consumed within the system, respectively. Stable isotope analysis was used to trace the fate of terrestrial and instream sources of organic matter in the aquatic food web. In a focal catchment in SE Queensland, additional measurements were taken of riparian attributes, catchment features and water quality. 3. Baseline measurements of GPP and R24 from undisturbed forest streams provided reference values for healthy streams for comparison with sites where the catchment o

Benthic metabolism as an indicator of stream ecosystem health

We tested direct and indirect measures of benthic metabolism as indicators of stream ecosystem health across a known agricultural land-use disturbance gradient in southeast Queensland, Australia. Gross primary production (GPP) and respiration (R-24) in benthic chambers in cobble and sediment habitats, algal biomass (as chlorophyll a) from cobbles and sediment cores, algal biomass accrual on artificial substrates and stable carbon isotope ratios of aquatic plants and benthic sediments were measured at 53 stream sites, ranging from undisturbed subtropical rainforest to catchments where improved pasture and intensive cropping are major land-uses. Rates of benthic GPP and R-24 varied by more than two orders of magnitude across the study gradient. Generalised linear regression modelling explained 80% or more of the variation in these two indicators when sediment and cobble substrate dominated sites were considered separately, and both catchment and reach scale descriptors of the disturbance gradient were important in explaining this variation. Model fits were poor for net daily benthic metabolism (NDM) and production to respiration ratio (P/R). Algal biomass accrual on artificial substrate and stable carbon isotope ratios of aquatic plants and benthic sediment were the best of the indirect indicators, with regression model R-2 values of 50% or greater. Model fits were poor for algal biomass on natural substrates for cobble sites and all sites. None of these indirect measures of benthic metabolism was a good surrogate for measured GPP. Direct measures of benthic metabolism, GPP and R-24, and several indirect measures were good indicators of stream ecosystem health and are recommended in assessing process-related responses to riparian and catchment land use change and the success of ecosystem rehabilitation actions

Flow intermittency, physico-chemistry and function of headwater streams in an Alpine glacial catchment

Erworben im Rahmen der Schweizer Nationallizenzen (http://www.nationallizenzen.ch)Relatively little is known regarding the extent of intermittent streams or the general ecology of headwaters in alpine catchments with glacial influence. This study quantified the contribution of intermittent streams to the total length of the stream network along with an ecological assessment during spring-summer of headwater streams (higher than 1,900 m above sea level) in the Val Roseg, a high Alpine glacial catchment. Stream network mapping revealed that ca. 90 % (76.8 km) of the drainage network consisted of intermittent streams. Glacier-fed headwaters experienced diel surface flows in late spring and summer, most going dry during the night due to reduced glacial inputs. In contrast, groundwater-fed streams often went dry in summer with the contraction of groundwater and other subsurface inputs. A principal components analysis of physico-chemical characteristics revealed headwaters to be primarily glacial-fed (kryal), groundwater-fed (krenal), or having a mixed water source. Although quite variable, periphyton biomass reached high levels (ca. 40 mg m-2 chla, 10 g m-2 AFDM) by late spring in most headwaters. Organic matter in transport (seston) ranged from 0.03 to 0.09 mg L-1 mostly consisting of fine particulate organic matter (FPOM: 33–76 %). Hyporheic sediment respiration rates varied considerably, ranging from 0.005 to 0.126 mg O2 h-1 kg-1 sediment and primarily related to the amount of loosely attached organic matter. These results indicate that intermittent streams are predominant in alpine landscapes, comprising mostly 1st to 2nd order systems, and that ecosystem properties vary substantially among headwater streams likely in relation to annual/daily changes in flow and water source. Such headwaters may contribute strongly to the production, processing and transport of organic matter to downstream waters, especially in light of the expected increase in intermittent streams in alpine catchments experiencing rapid glacial recession