Isotopic Assessment of Sources of Surface Water Nitrate within the Oldman River Basin, Southern Alberta, Canada

Concentrations and isotopic compositions of NO-3 from the Oldman River (OMR) and some of its tributaries (Alberta, Canada) have been determined on a monthly basis since December 2000 to assess temporal and spatial variations of riverine NO-3 sources within the OMR basin. For the OMR sites, NO-3 -N concentrations reached up to 0.34 mg L-1, d15N-NO-3 values varied between –0.3 and +13.8‰, and d18O-NO-3 values ranged from –10.0 to +5.7‰. For the tributary sites, NO-3 -N concentrations were as high as 8.81 mg L-1, d15N-NO-3 values varied between –2.5 and +23.4‰, and d18O-NO-3 values ranged from –15.2 to +3.4‰. Tributaries in the western, relatively pristine forested part of the watershed add predominantly NO-3 to the OMR with d15N-NO-3 indicative of soil nitrification. In contrast, tributaries in the eastern agriculturally-urban-industrially-used part of the basin contribute NO-3 with d15N-NO-3 values of about +16‰ indicative of manure and/or sewage derived NO-3. This difference in d15N-NO-3 values of tributaries was found to be independent of the season, but rather indicates a spatial change in the NO-3 source, which correlates with land use changes within the OMR basin. As a consequence of tributary influx, d15N-NO-3 values in the Oldman River increased from +6‰ in the downstream direction (W to E), although [NO-3 -N] increased only moderately (generally

Factors influencing the distribution of native and introduced Gammarus spp. in Irish river systems

Populations of Gammarus duebeni celticus, previously the only amphipod species resident in the rivers of the Lough Neagh catchment, N. Ireland, have been subjected to invasion by G. pulex from the British mainland. Numerous previous studies have investigated the potential behavioural mechanisms, principally differential mutual predation, underlying the replacement of G. d. celticus by G. pulex in Irish waters, and the mutually exclusive distributions of these species in Britain and mainland Europe. However, the relative degree of influence of abiotic versus biotic factors in structuring these amphipod communities remains unresolved. This study used principal component analysis (PCA) to distinguish physico-chemical parameters that have significant roles in determining the current distribution of G. pulex relative to G. d. celticus in L. Neagh rivers. We show that the original domination of rivers by the native G. d, celticus has changed radically, with many sites in several rivers containing either both species or only G. pulex. G. pulex was more abundant than the G. d. celticus in sites with low dissolved oxygen levels. This was reflected in the macroinvertebrate assemblages associated with G. pulex in these sites, which tended to be those tolerant of low biological water quality. The present study thus emphasizes the importance of the habitat template, particularly water quality, for Gammarus spp. interactions. If rivers become increasingly stressed by organic pollution, it is probable the range expansion of G. pulex will continue. Because these two species are not ecological equivalents, the outcomes of G. pulex incursions into G. d. celticus sites may ultimately depend on the prevailing physico-chemical regimes in each site.

Sediment changes upstream and downstream of the Altnahinch Dam in the River Bush in Northern Ireland: A preliminary study

The River Bush must reach a standard of good ecological potential (GEP) by 2015 due to the requirements of the water framework directive. The role of sediments within a water body is extremely important to all aspects of a river's regime. The aim of this research is to investigate the effects of Altnahinch Dam on sediment distribution in the River Bush (a heavily modified water body) with comparison made against the Glendun River (an unmodified water body). Samples collected from the rivers were analysed by physical (pebble count, sieve analysis) and statistical methods (ANOVA, GRADISTAT). An increase in fine sediments upstream of the dam provides evidence that the dam is impacting sediment distribution. Downstream effects are not shown to be significant. The output of this study also implies similar impacts at other drinking water storage impoundments. This research recommends that a sediment management plan be put in place for Altnahinch Dam and that further studies be carried-out concentrating on fine sediment distribution upstream of the dam. 

Fluxes of organic contaminants from the river catchment into, through and out of the Humber Estuary, UK

This paper summarises the work done on the distribution and reactivity of organic contaminants (simazine, atrazine, lindane, fluoranthene, pyrene, PCB 77, PCB 118) in the Humber Estuary and associated major rivers, as part of the LOIS programme. The preliminary flux calculations show that the most important contributors of selected organic contaminants were the rivers Trent (45% of simazine, 20% of atrazine), Aire (30% of simazine and 33% of atrazine), Don (36 and 37% of fluoranthene and pyrene) and Ouse (18% of fluoranthene and pyrene). For lindane and PCBs, the Aire and Ouse were the key sources. The water flow in all the rivers shows strong seasonal variations, as do the contaminant concentrations. As a result, the mean daily fluxes of these contaminants displayed a strong seasonality. Annual mean concentrations of simazine and atrazine decreased by more than 50% over the period 1994-1995 in most of the rivers, probably as a result of their restricted use in the UK. Mass balance calculations show that the Humber is a sink for atrazine, lindane, PCB 77 and PCB 118, although the degree of removal is generally much lower for atrazine and lindane than for PCB 77 and PCB 118. Mass balance results also show that the Humber can either be a source of fluoranthene and pyrene (in the suspended particulate phase), or a sink (in the dissolved phase), although overall the Humber acts as sink. The budget exercise represents an attempt to quantify the input and output of selected organic contaminants from catchment to ocean. However, due to limited data and assumptions involved in calculations, the estimates should be considered as an order of magnitude approximation. Further improvement both in resolution and accuracy is required.