Tracing nitrate and sulfate in river basins using isotope techniques

The objective of this paper is to outline how stable isotope techniques can contribute to the elucidation of the sources and the fate of riverine nitrate and sulphate in watershed studies. The example used is the Oldman River Basin (OMRB), located in southern Alberta (Canada). Increasing sulphate concentrations and decreasing d34S values along the flowpath of the Oldman River indicate that oxidation of pyrite in tills is a major source of riverine sulphate in the agriculturally used portion of the OMRB. Chemical and isotopic data showed that manure-derived nitrogen contributes significantly to the increase in nitrate concentrations in the Oldman River and its tributaries draining agricultural land. It is suggested that hydrological conditions control agricultural return flows to the surface water bodies in southern Alberta and impart significant seasonal variations on concentrations and isotopic compositions of riverine nitrate. Combining isotopic, chemical, and hydrometric data permitted us to estimate the relative contribution of major sources to the total solute fluxes. Hence, we submit that isotopic measurements can make an important contribution to the identification of nutrient and pollutant sources and to river basin management.

Nitrogen budget for the Oldman River Basin, southern Alberta, Canada

The Oldman River Basin (OMRB), located in southern Alberta (Canada), with an area of 28,200 km2, is mainly forested in its western part and is used for intensive agriculture in its eastern part. The objective of this paper is to estimate the nitrogen (N) budget for the Oldman River Basin as a whole and its sub-basins, and to discuss differences in the N budget between various sub-basins. Better knowledge of the N budget in this watershed may be also utilized for understanding N dynamics in similar watersheds within semi-arid climatic regions. The model used is a mass balance spreadsheet model that takes into account N inputs and N export through surface water. During the last 120 years, anthropogenic N inputs to the OMRB have increased circa 40 fold. By the end of the 20th century, the OMRB received an annualN input of about 5174 kg N km-2 yr-1, whereas only about 25 kg N km-2 yr-1 were exported via riverine flow. For the sub-basins, annual N inputs ranged from 2516 to 19011 kg N km-2 yr-1, and annual N export via riverine flows varied between 6 and 277 kg N km-2 yr-1. Over 85% of total N inputs to the OMRB are due to anthropogenic activities, including manure (55%), synthetic fertilizer (27%), and N fixation on agricultural lands (4%). Sewage accounted for less than 1%, and N inputs from atmospheric deposition and fixation in forests represented 6 and 8% respectively. Despite increasing anthropogenic N inputs, N export with riverine flow currently accounts for only 1% of the inputs, indicating thatmost of theNinputs are currently retained in the OMRB or are re-emitted into the atmosphere.

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.

Demographics and landscape features determine intrariver population structure in Atlantic salmon (Salmo salar L.): the case of the River Moy in Ireland

Contemporary genetic structure of Atlantic salmon (Salmo salar L.) in the River Moy in Ireland is shown here to be strongly related to landscape features and population demographics, with populations being defined largely by their degree of physical isolation and their size. Samples of juvenile salmon were collected from the 17 major spawning areas on the river Moy and from one spawning area in each of five smaller nearby rivers. No temporal allele frequency differences were observed within locations for 12 microsatellite loci, whereas nearly all spatial samples differed significantly, suggesting that each was a separate population. Bayesian clustering and landscape genetic analyses suggest that these populations can be combined hierarchically into five genetically informative larger groupings. Lakes were found to be the single most important determinant of the observed population structure. Spawning area size was also an important factor. The salmon population of the closest nearby river resembled genetically the largest Moy population grouping. In addition, we showed that anthropogenic influences on spawning habitats, in this case arterial drainage, can affect relationships between populations. Our results show that Atlantic salmon biodiversity can be largely defined by geography, and thus, knowledge of landscape features (for example, as characterized within Geographical Information Systems) has the potential to predict population structure in other rivers without an intensive genetic survey, or at least to help direct sampling. This approach of combining genetics and geography, for sampling and in subsequent statistical analyses, has wider application to the investigation of population structure in other freshwater/anadromous fish species and possibly in marine fish and other organisms.

A PRELIMINARY ASSESSMENT OF THE DISTRIBUTION OF THE SEA LAMPREY (PETROMYZON MARINUS L.), RIVER LAMPREY (LAMPETRA FLUVIATILIS (L.)) AND BROOK LAMPREY (LAMPETRA PLANERI (BLOCH)) IN NORTHERN IRELAND

Lampreys are endangered in Europe, and European states are legally required to take measures to ensure their protection. However, there is currently little information on the distribution of the three species present in Northern Ireland. Anecdotal records of adult lampreys were collated from anglers and other sources, and a systematic electrofishing survey was undertaken to establish the distribution of lamprey ammocoetes. Lampreys were found in seven of the nine Northern Irish river catchments. Brook lampreys (Lampetra planeri (Bloch)) were widely distributed, but the two anadromous species, sea lamprey (Petromyzon marinus L.) and river lamprey (Lampetra fluviatilis (L.)), were more limited in their distribution, possibly due to barriers restricting migration.