Intensive measurements of the fluxes of phosphorus (P) and of P retention were carried out in a Danish lowland watershed (Gjern A) during two hydrological years (June 1987to May 1989. Seasonal and short-term variations of P concentrations were measured by intensive automatic sampling covering P fluxes from the entire Gjern A watershed and two subcatchments: the Gelbaek and Lake SsbygBrd. Moreover, infrequent sampling was performed in all major tributaries of the river system. Transport of P compounds (dissolved and particulate P) exposed a seasonal pattern which was highly affected by flow conditions, instream processes, as well as point and non-point sources. Stormflow P transport during the two study years (1987-8 and 1988-9) constituted 56 and 61 ' YO in the Gelbzk, respectively, compared with 25 and 23% in the Gjern A, respectively. Particulate P transport in the Gelbrek constituted 56 and 75% of annual total P transport during the two years compared with 77 and 75% in the Gjern A. The magnitude of monthly baseflow and stormflow total P loads was significantly correlated with the mean monthly discharge during baseflow and stormflow in the Gelbzek, whereas only stormflow loads were correlated to discharge in the Gjern A. In situ measurements of retention showed that the maximum amount of P stored in the GelbEk during summer (June to August) was 22 gPm-2 (1988) compared with 27gPm-2 (1987) in the Gjern A. Lake SarbygHrd was a P source during summer but a P sink during winter and on an annual basis the net P released was 810 and 1420 kg, which corresponded to 7 and 20% of the annual P export from the watershed, respectively. Retention constituted about 30% of gross P transport in the Gelbaek during summer compared with 20% in the Gjern A. Resuspension of retained P during stormflows in September 1987 constituted 94% of the stormflow P transport and 54% of the total P transport. Monthly total P and dissolved reactive P (DRP) mass balances for the main channel of the Gjern A revealed a significant DRP retention over 17 months (p < 0.05) caused by P adsorption on sediments and biological uptake. On an annual basis the main channel was a sink of DRP (1220 and 1660kg P) but a source of total P (3440 and 1000 kg P), implying that the channel is an important source of particulate P. Bank erosion proved to be a significant P source in the main channel of Gjern A, whereas P delivery from soil erosion was possibly of minor importance. The annual non-point P export from two intensively sampled catchments was significantly higher (0.89 and 0.45 kgP ha-' yr-') than from the five extensively sampled subbasins (0.43 and 0.17 kg P ha-' yr-I). No significant relationship could be established between non-point P export and the proportion of arable land and soil type. Only for the wet year of 1987-8 was a significant relationship established between non-point P export and the P load from scattered dwellings outside sewage areas in five subbasins.
No abstract
1. Macroinvertebrates were collected and physico‐chemical variables measured at 16 stream sites in Western Greenland during July 1999. Eight sites were located on Disko Island in an arctic oceanic climate and eight sites in the Kangerlussuaq area close to the icecap where the climate is arctic continental. The streams had different water sources (glacial, groundwater, snowmelt and lake water). 2. The streams showed pronounced differences in water temperature (2.2–17.3 °C), concentrations of suspended solids (0–2400 mg L−1), and conductivity (10–109 μS cm−1). Principal component analysis (PCA) analysis of the physico‐chemical variables separated the Disko Island sites into a distinct group, whereas the sites in the Kangerlussuaq area were more dispersed. 3. A total of 56 macroinvertebrate species were found, including 31 species of Chironomidae, the most abundant of which was Orthocladius thienemanni. Diamesa sp. was only the sixth most abundant chironomid taxon. Species composition varied between sites, and abundance varied from about 20 individuals m−2 in a glacier fed stream to more than 16 000 m−2 in a lake outlet. 4. The macroinvertebrate communities of the 16 streams were separated into five TWINSPAN groups reflecting water source, irrespective of region. Lake outlets and ground‐water‐fed streams had the highest species richness and abundance, temperature and bed stability, while glacier‐fed streams were characterized by low species richness, abundance, temperature, bed stability and high concentrations of suspended solids. Macroinvertebrate species richness was positively correlated with water temperature and negatively with bed stability. Conductivity was positively correlated with invertebrate abundance. 5. The results of this study suggest that the source of stream water can be used to predict invertebrate community composition in Greenlandic streams and thus the effects of changes in water balance and flow regime, and to identify sites of special conservation interest.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.