University Of Tasmania
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Monitoring river catchments in relation to potential environmental impacts from aquaculture activities

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posted on 2023-05-28, 08:50 authored by Tran, TMT
Numerous factors affect stream macroinvertebrate communities including river geomorphology, natural habitat within the catchment and human influences. In Tasmania Australia, a number of salmonid hatcheries discharge aquaculture effluent into adjacent rivers but the impacts of this waste water on macroinvertebrate communities of these receiving waters is not well known despite being essential for informing management options. In this thesis, I examined spatial and temporal patterns in macroinvertebrate communities in rivers with and without aquaculture farms from two regions of Tasmania (north and south) across multiple times to assess the evidence for impacts of farms on macroinvertebrate communities. I also assessed the impacts of a major flood on macroinvertebrate communities in rivers. I then explored the potential for this information to be used as a simple, quick and reliable monitoring tool for aquaculture farms wishing to manage and monitor waste discharge effluents on streams. The first data chapter (Chapter 2), describes differences in macroinvertebrate communities in rivers without farms in the northern and southern regions of Tasmania and across time to assess background patterns of macroinvertebrate community structure in Tasmanian rivers. Macroinvertebrate community composition was not different between the two regions but differed significantly among rivers reflecting differences in stream geomorphology, natural habitat of the catchment, and biological conditions (source of pollution). Four upland rivers surrounded by forest all had a similar community structure which indicated good water quality while four lowland rivers surrounded by grazing and agriculture had a different community structure (but were similar to each other) which suggested they were mildly polluted. Finally, two small, shallow lowland rivers with high levels of anthropogenic impacts (grazing, agriculture, urbanised and industrial areas) surrounding them had significantly different invertebrate community structure from all other sites. Certain taxa including Chironomidae (midges), Hirudinae (leeches), Planorbidae (snails), Physa acuta (air-breathing freshwater snails), Cura sp.(flat worms), Ceinidae (amphipods), Paramelitidae (amphipods) and Oligochaeta (aquatic worms) were indicators for sites rated as mild to moderate pollution (lowland rivers) while Scirtidae (beetles), Hydrobiosidae (caddisflies), Leptophlebiidae (mayflies), Eusthenia costalis (stoneflies), and Elmidae (beetles) were indicative of cleaner sites (upland rivers). The spatial differences in communities among rivers were mostly due to differences in number of each taxa within community. The temporal comparison showed that there were similarities in invertebrate community between summer and autumn as well as between winter and autumn. The largest temporal differences in communities occurred prior and post a large flood event highlighting the role of natural disturbance in affecting stream macroinvertebrate communities. Chapter 3 compared the macroinvertebrate communities in autumn 2016 in northern and southern streams with and without farms to examine the impacts of farm effluents at the farm outlet on the receiving stream. Outfalls at the aquaculture sites at Patricks, Brumbys, Russell Falls and Florentine showed similarities in community structure with high numbers of pollution tolerant species (Oligochaeta, Planorbidae, Physa acuta, Sphaeriidae (freshwater bivalve molluscs), Hirudinae, and Chironomidae) but significant differences to upstream reference sites as well as other non-aquaculture sites, highlighting the impacts of nutrient waste in aquaculture effluent on receiving waters. Furthermore, outfalls on Brumbys and Florentine appeared to have a greater impact than outfalls on the Patricks and Russell Falls sites. In contrast, the Broad as well as the upstream sites of Patricks, Russell Falls and all surrounded by forest had a similar community structure and were the cleanest sites with high numbers of Eusthenia costalis, Baetidae and Scirtidae. The community structure of the upstream reference site on the Brumbys was similar to the non-aquaculture Derwent, Dee and Ouse while the Tyenna End and the Styx also showed similar community structure. These six sites indicated mild to moderate pollution, highlighting the presence of other sources of pollution. Chapter 4 determined the differences in macroinvertebrate communities among stations at different distances downstream from the farm outlet in Brumbys Creek and Florentine River over four seasons to describe the level of impact and degree of recovery. The most impacted stations were at the waste discharge point and station immediately below, which showed significant differences in macroinvertebrate community structure from other stations. Those two stations had high numbers of pollution tolerant species, high numbers of total individuals; but lower taxa richness and lower diversity. Although macroinvertebrate composition of the stations further downstream differed from upstream and outlet stations; the communities overlapped suggesting a recovery in the health of the stream moving downstream. However, this was only observed > 800m from the outlet. In terms of indicators species, Psephenidae (water-penny beetles), Gripopterygidae (stoneflies), Eusthenia costalis (stoneflies), Ceinidae, Elmidae, Baetidae, Paramelitidae and Leptoplebiidae were indicative of non-farming conditions (upstream stations); Oligochaeta, Planorbidae, Physa acuta, Hirudinae and Ancylidae (air-breathing limpets) were indicators of polluted conditions at the outlet and just below the outlet; while Orthocladiinae (midges), Tanypodinae (midges), Chironominae (midges) and Hydropsychidae were indicative of mild pollution in stations further downstream. Chapter 5 describes the correlation between stream macroinvertebrate communities and physical water parameters. The first objective was to examine whether water chemistry might be a proxy for the macroinvertebrate communities in Tasmania or if specific macroinvertebrates might actually be the best (most cost-effective) tool for a monitoring program. The second objective was to determine potential bioindicators correlated with specific water parameters to use as a simple and quick tool for farms to manage and control aquaculture impacts. There was a relationship between macroinvertebrates and water quality chemistry. The less disturbed sites (upland rivers) had a higher abundance of pollution intolerant taxa (notably Psephenidae, Baetidae, Eusthenia costalis, Gripopterygidae, Atalophlebia australis, Costora Delora, Lingora sp. and Scirtidae) which correlated with DO and pH levels greater than 9 mg/l and 7 respectively and indicated good water quality. Aquaculture sites appeared to have markedly higher nitrogen and phosphorus concentrations compared to other sites with ammonia, nitrate, nitrite, nitrate & nitrite, total phosphorus at farming sites ranging from 210 ‚Äö- 580 ug/l, 0.06 ‚Äö- 0.17 mg/l, 0.011 ‚Äö- 0.25 mg/l, 72- 200 ug/l, and 40 ‚Äö- 80 mg/l respectively. These high concentrations were correlated with high abundances of Oligochaeta, Planorbidae, Physa acuta, Cura sp. and Hirudinae. Tipulidae (crane fly), Ceinidae, Paramelitidae, Caenidae (mayflies), Hydrobiosidae (caddisflies), Ecnomidae (caddisflies), Sciomyzidae (marsh flies), Hydroptilidae (caddisflies), and Calamoceratidae (caddisflies), suggesting these taxa were indicators for agriculture and grazing sites (lowland rivers). Nevertheless, water chemistry showed no marked differences between agriculture sites (alternative sources of impacts) and the clean forest sites; while macroinvertebrates were different between these sites suggesting macroinvertebrates may be better than water chemistry in terms of a monitoring tool. In summary, the results of this study have increased the understanding in Tasmania of how macroinvertebrates respond to different geomorphology, natural habitat and pollutants and can identify recovery at distances moving downstream from the outfalls. The major flood that occurred in 2016 had a significant influence on macroinvertebrates at both aquaculture and non-aquaculture sites in the southern region, with different macroinvertebrate communities observed after the flood, in contrast to only a slight impact on communities in the northern region. Aquaculture effluents had potential impacts on rivers; however, the level of impact decreased moving downstream from the outfalls. Overall, the recovery level appears to depend on the amount of waste discharge, stream conditions and the distance from impacted points. Therefore, establishing stream baseline standards is important to evaluate both impact and recovery processes. Finally, using indicators species appears to be a quick, simple and cost-effective tool to assist aquaculture farms wishing to assess and monitor effluents for management and regulatory purposes. Instead of looking at the whole community at a site, the presence and the degree abundance of taxa such as Oligochaeta can indicate the degree of pollution.


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