Agricultural activities release variable products into air, soil and water ecosystems. The study was conducted to evaluate the impact of agriculture and concentrated livestock operations on stream and lake water quality in Grand Lake St. Marys watershed of north-western Ohio. Temporal water samples from the lake and the 6 feeding streams were collected bimonthly from January 2005 to May 2007, processed and measured for temperature, turbidity, pH, electrical conductivity (E C ), ammonium NH þ 4 À Á , nitrate NO À 3 À Á , dissolved phosphorus (P), ultra-violet (UV) light absorption, and dissolved oxygen (DO), employing standard methods of analysis. The measured data were normalized and integrated into a simple index (WQ Index ) to evaluate overall water quality. Results showed that over 90% of the area in the watershed was under cropland with associated livestock operations. With a land area equal to 195 km 2 represented by the six major tributaries, the average animal density was over 240 units km −2 . As a result, land disposal of manure from confined feedings operations and direct deposit by grazing animals contributed to non-point sources of water pollution. While NH þ 4 À Á and P concentration, turbidity, and UV absorption peaked during the summer, the NO À 3 À Á and DO concentration in both stream and lake water was lowest in the summer. Water sampled from the Coldwater, Beaver and Prairie creeks had higher turbidity, NH þ 4 À Á , and P than other creeks. However, DO concentration and UV absorption of water did not change significantly by the influence of streams. The WQ Index peaked in both streams and lake water with greater water quality degradation in Beaver and Coldwater creek than other creeks. A significant relationship of WQ Index with UV absorption and P accounted 84 to 90% of the variations in stream and lake water quality degradation. However, a strong linear relationship (r 2 =0.81; p<0.01) between UV absorption and P concentration suggested a major contribution of P to the degradation of stream and lake water quality through algal blooming and associated eutrophication.
Riverine food webs are often laterally disconnected (i.e. between watercourses) in regulated floodplain wetlands for prolonged periods. We compared the trophic structure of benthic resources and consumers (crustaceans and fish) of the three watercourses in a regulated floodplain wetland (the Gwydir Wetlands, Australia) that shared the same source water but were laterally disconnected. The crustaceans Cherax destructor (yabby), Macrobrachium australiense (freshwater prawn), the exotic fish Cyprinus carpio (European carp) and Carassius auratus (goldfish) showed significantly different δ13C values among the watercourses, suggesting spatial differences in primary carbon sources. Trophic positions were estimated by using δ15N values of benthic organic matter as the base of the food web in each watercourse. The estimated trophic positions and gut contents showed differences in trophic positions and feeding behaviours of consumers between watercourses, in particular for Melanotaenia fluviatilis (Murray–Darling rainbowfish) and M. australiense. Our findings suggest that the observed spatial variation in trophic structure appears to be largely related to the spatial differences in the extent and type of riparian vegetation (i.e. allochthonous carbon source) across the floodplain that most likely constituted part of the benthic resources.
On Australian semiarid floodplains, large herbivores such as kangaroos have a role in the cycling of energy (carbon) through the mechanism of feeding and defaecation of vegetative material. The degree to which kangaroos are vectors of energy within this system is not fully understood. This study describes the stable carbon isotope signature of floodplain plants and kangaroo scats at two close study sites. Kangaroos were found to deposit scats that mirrored the forage composition at each particular feeding site. Scats were 3.94‰ higher in δ13C values at the site where C4 grasses were available, indicating that this grass contributed ~25–30% of the diet of these kangaroos. The difference in diet due to the relative availability of C3 and C4 forage, detectable in the carbon stable isotope signature of scats, is used to demonstrate that kangaroos are recycling and redistributing energy locally, rather than transporting it more broadly across the floodplain.
A field survey was conducted during flow pulses to investigate the longitudinal spatial patterns in water quality, dissolved inorganic and organic matter, phytoplankton, planktonic bacteria, zooplankton, gross primary productivity (GPP) of phytoplankton and planktonic respiration (PR) in channels of the large floodplain system ($124 km in length) of the Macquarie Marshes, south-eastern Australia. Four river reaches (areas) with distinct hydrogeomorphological characteristics within the distributary zone of the lower Macquarie River were chosen for analysis of abiotic and biotic variables in their in-stream environments. The results showed marked longitudinal spatial variation in the values within and among the measured environmental variables including such functional aspects as primary productivity and PR. The variables that tended to have increasing values in a downstream direction were conductivity, total nitrogen (TN), total phosphorus (TP), dissolved reactive phosphorus (DRP), dissolved silica, dissolved organic carbon (DOC), dissolved organic nitrogen (DON), dissolved organic phosphorus (DOP), ratio of DOC/DON and counts of planktonic bacteria. Conversely, the values that tended to decrease downstream were the ratios of TN/TP, DIN/DRP, DOC/DOP, DON/DOP and GPP/PR. Variables that had a localized peak(s) were dissolved oxygen, turbidity, dissolved inorganic nitrogen, GPP, PR and counts of cyanobacteria, diatoms, green algae, cryptomonads, protozoans, rotifers, copepods and cladocerans. Overall, two distinct ecological zones were identified within the broader distributary functional process zone (FPZ): these being the upstream zone with relatively high levels of DO, turbidity, diatoms and GPP/PR ratio, and the downstream zone with relatively high levels of nutrients, dissolved organic matter, cyanobacteria, planktonic bacteria, protozoans and cladocerans. The results of this study describe the spatial connectivity of ecological processes related to hydrogeomorphological factors within a FPZ of a riverine ecosystem, and support the predictions of the riverine ecosystem synthesis framework that ecological patterns and processes can be discontinuous on a longitudinal spatial scale.
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