Academic literature on the topic 'Aquatic ecology Victoria Loch River'

Phytoplankton was sampled on a monthly basis for 1 year at five stations on the La Trobe River in Gippsland, Victoria. In the upper, mostly forested, reaches of the river, chlorophyll a concentrations and cell densities were uniformly very low, and the dominant algae were detached benthic diatoms and flagellated species. In the plains section of the river, downstream of an impoundment (Lake Narracan), spring and autumn blooms occurred, with a marked reduction in abundance in midsummer and midwinter. The lowland planktonic flora was dominated by centric diatoms, particularly Melosira distans in autumn and Skeletonema potamos in spring.

Diel oxygen-curve techniques were used to estimate gross primary productivity (PG), community respiration and net daily metabolism (NDM) for five reaches of the La Trobe River from headwaters to lowlands. All reaches were heterotrophic throughout the study (December 1980-November 1981) with NDM ranging from - 1 to -6 g O2 m-2. PG was consistently very low at the most upstream station and highest in the middle reaches of the river, where both benthic and planktonic contributions were important. At the most downstream station benthic productivity was negligible but planktonic productivity was appreciable in spring and autumn. PG in the river may be limited in the upper reaches by lack of light (due to shading by vegetation) and low levels of nutrients, and in the lower reaches by turbidity and increased depth.

The importance of aquatic arthropods in the processing of organic matter in fluvial systems is well known, but this topic has been poorly studied in Neotropical rivers. In this research, we studied the composition of functional feeding groups (FFGs) associated with differences in elevation in a tropical river in northern Colombia during the wet and dry seasons. Between 2008 and 2013, we collected benthic arthropods at 3 sites located in the upper (San Lorenzo), intermediate (La Victoria) and lower (Puerto Mosquito) sections of the Gaira River. We found some differences in the gut contents and FFGs of the animals from different sites and between the climatic seasons. The dominant food source at all the sites and during both seasons was fine particulate organic matter (FPOM). At La Victoria, the genera Leptonema, Smicridea and Phylloicus (all belonging to Trichoptera) presented significant differences in the consumption of coarse particulate organic matter (CPOM) between the rainy and dry seasons (p < 0.05). At San Lorenzo, Leptonema had the highest animal tissue consumption value (p < 0.05). A discriminant function analysis based on gut contents suggested that some taxa may have been assigned to the wrong FFGs. We concluded that the diets of the aquatic arthropods in our study tended to present high trophic plasticity. Consequently, our results suggest that Neotropical rivers need to be re-evaluated in terms of traditionally established FFGs, which heretofore have been based on information from other regions of the world, producing incorrect assessments of aquatic systems.

Annual production was estimated by the size-frequency method for Ephemeroptera (Tasmanocoenis tonnoiri, two species of Baetis, Atalonella spp., Atulophlebioides sp.), Plecoptera (Leptoperla spp.) and Trichoptera (Ecnomus sp.) at four sites on the lowland section of the La Trobe River. Annual production (P) of individual ephemeropteran species (or genera) varied from 0.02 to 0.7 g m-2 while total annual production of this order at two sites was 0.7-1 . 5 g m-. Annual production of Leptoperla spp. was 0.03 g m-2 at one site while Ecnomus sp, averaged 2 g m-2 at two sites. Estimates of annual production were subject to an error of at least t 50%. Annual turnover ratios (P/B; B is mean biomass) varied from 9 to 19 and were three to four times higher than published values for similar-sized macroinvertebrates in the temperate zone (generally < 15°C mean annual habitat temperature). This probably resulted from the higher average temperatures (17-18°C) at most sites.

Salinity levels are rising in many freshwater environments, yet there are few direct measurements of salinity tolerance of organisms likely to be salt sensitive. The relative salinity tolerance to artificial seawater of macroinvertebrates from the Barwon River in Victoria, Australia, was assessed by measuring the 72-h lethal concentrations required to kill 50% of individuals (LC50). LC50 values ranged from an electrical conductivity of 5.5 to 76 mS cm–1 (mean 31 mS cm–1, n = 57) and followed a log-normal distribution. The most salt-sensitive groups tested were Baetidae (LC50 value range: 5.5–6.2 mS cm–1), Chironomidae (10 mS cm–1) and several soft-bodied non-arthropods (Oligochaeta, Gastropoda, Nematomorpha, Tricladida and Hirudinea; 9–14 mS cm–1). Other groups, from least to most tolerant, were non-baetid Ephmeroptera (>12.6–15 mS cm–1), Plecoptera (>12.6–>20 mS cm–1), Trichoptera (9–>26 mS cm–1), Corixidae (18–26 mS cm–1), non-corixid Hemiptera (33–44 mS cm–1), Coleoptera (19–54 mS cm–1), Hydracarina (39 mS cm–1) and Odonata (30–55 mS cm–1), and macrocrustaceans (Decapoda, Isopoda and Amphipoda; 38–76 mS cm–1).

Densities of carp, ranges of turbidity, and details of communities of aquatic vegetation from 1979 to 1982 are given for several waterbodies in the Goulburn River valley including the Broken River, near Shepparton, Victoria. The turbidity values at all sites were high, typical of Australian inland waterbodies. There was no association between high carp densities and high turbidity, and populations of carp did not appear to increase turbidity. Observed turbidity increases at each site appeared to be related to hydrological changes. Fluctuation of water levels was also an important factor determining the extent of aquatic vegetation communities. However, circumstantial evidence is presented that shallow-rooted and soft-leaved aquatic vegetation such as Potamogeton spp. have been reduced by carp.

Life history studies were carried out for populations of six species of Leptoceridae. Study sites were a permanent river (Acheron), a temporary river (Lerderderg) and a permanent lake (Monash University). Life histories varied in degree of synchrony of larval development, in length of adult emergence period, and from bi- to semivoltine. Oviposition requirements of adults were found to be the major factor influencing synchrony of the life history of one species. Life history features did not ameliorate the effects of the severe drought of 1982-83, nor did drought result in large changes in life histories.

Between February 1975 and March 1977, periphyton from artificial substrata (glass microscope slides) and water samples for physicochemical analysis were obtained from eight sites on the lowland section of the La Trobe River, which flows through agricultural, urban and industrial areas. Total organic matter on the slides, estimated as weight loss on ignition, was usually highest in summer or autumn when river flows were low. However, chlorophyll a densities generally peaked in late winter and spring when nitrate concentrations were high, except at a site upstream of major urban and industrial areas, where a summer-autumn increase occurred. Thermal discharges from major power stations had no obvious effect on chlorophyll abundance, but did appear to substantially influence diatom assemblage composition from late summer to early winter, when river temperatures were highest. Downstream of the Morwell River confluence, diatom assemblages were influenced by a sharp increase in dissolved solids concentration and probably also by the grazing activities of snails (Ferrissia petterdi and Physastra gibbosa). The diatom flora at the most downstream site showed some evidence of recovery from thermal effects.

Australian bass (Macquaria novemaculeata) and estuary perch (M. colonorum) are very similar in their morphology, use of habitat and geographical distribution. Following the capture from four Victorian rivers of specimens possessing species-diagnostic attributes intermediate to the two taxa, an allozyme electrophoresis and morphometric study was undertaken to investigate the possibility that these individuals were the results of interspecific hybridization. Two allozyme loci were found to be useful in species identification and were used to confirm that the individuals in question were indeed interspecific hybrids. The presence of hybrids was further supported by univariate and multivariate analysis of morphological characters. Temperature-gradient gel electrophoresis on mtDNA control- region fragments demonstrated that where interspecific hybrids were identified, the maternal parent species was M. novemaculeata. The demonstration that M. novemaculeata and M. colonorum can hybridize in natural populations emphasizes the importance of correct species identification in breeding programmes to prevent the liberation of large numbers of interspecific hybrids.

Eleven stream stations within the basins of the Bemm, Cann, Thurra, Wingan and Genoa Rivers were sampled during a 3-month interval following a prolonged drought and intense and extensive forest fires. Emphasis was placed on flows resulting from three major storms that occurred during this period. Water-quality impacts of the fires were intermingled with those of the preceding drought, and flow- related comparisons with pre-drought data showed appreciable increases in colour, turbidity, suspended solids, potassium and nitrogen levels in the Bemm River, which was only marginally affected by the fires. In the Cann and Genoa Rivers, with much larger proportions of catchment burnt, electrical conductivity and phosphorus concentrations also rose substantially. Marked depletion of dissolved oxygen (to <6 mg I-1) was unique to streams with burnt catchments, but resulted from stagnant conditions at the end of the drought as well as from changes occurring at the time of the first post-fire storm. The fires had little obvious effect on temperature and pH regimes. Peak turbidities and concentrations of suspended solids and phosphorus were much greater in the Cann and Genoa river systems than elsewhere. Maximum values for these indicators were 130 NTU, 2300 mg I-1 and over 0.8 mg I-1, respectively. In the Thurra and Wingan basins, which were also burnt, stream suspended-solids levels were lower (<200 mg I-1), but solutes sometimes reached very high maxima (indicated by peak electrical conductivities of up to 110 mS m-1). Variations in catchment topography and soils and the relative importance of surface and subsurface flow probably account for these differences. The first post-fire storm produced the highest measured levels of many indicators in most streams, although the greatest flows were associated with the third storm. Nitrite and ammonia were notable exceptions to this generalization. Estimates of catchment exports indicated high sediment yields and moderate to high phosphorus yields from the Cann and Genoa catchments, by comparison with other Australian data.