Abstract:

As land use is an important factor controlling outputs and stoichiometric proportions of soil nutrients in runoff from a catchment and hence affecting service functions of the various ecosystems within the catchment, determination of nutrient contents and their bio-stoichiometric proportions in runoff have become an important tool for evaluating ecological processes and waterbody nutrient status of the catchment. In order to follow variations of nitrogen and phosphorus concentrations and their stoichiometric proportions in runoffs with type of landscape in the Chaihe Catchment of the Dianchi Lake, water qualities were monitored spatio-temporally in the landscapes dominant of the catchment. Results show that (1) the surface runoff waters in the catchment were all far beyond the criteria of the national standard for water environment quality in China in N and P concentrations, and the pollutants existed mainly in the form of dissolved nitrogen and particulate phosphate; (2) nitrogen content in runoff in flatlands and phosphate content in runoff in the phosphorus mining areas varied quite sharply temporally, while nitrogen content in runoff did spatially in the early period of the wet season and phosphorus content did in the mid-wet season; and (3) according to previous studies, in which N:P ＜ 7 and ＞ 30 were set for grading of waterbodies in quality for limiting nutrients in runoff, the surface runoffs from flatlands and tablelands as a whole, were under the condition of phosphorus limitation and the surface runoff from the phosphate mining areas and forestlands in phosphorus-rich areas were under the condition of nitrogen limitation, while the runoffs in the greenhouse regions and the lower reaches of the Chaihe River was under the condition of none-limitation. It is, therefore, concluded that the effluent of the Chaihe River flowing into the Dianchi Lake tends to intensify the eutrophication risk of the Dianchi Lake.

Key words: landscape type, nutrient stoichiometry, tempo-spatial variation, eutrophication, Chaihe catchment