Long-Term Trends in the Nutrient Input and In-Lake Concentrations of a Drinking Water Reservoir in a Dense Populated Catchment Area (Erzgebirge,Germany)

The concentrations of soluble reactive and total phosphate, silicate, and nitrate in the tributaries and in the watercolumn of the meso/eutrophic reservoir Saidenbach were investigated at weekly or fortnightly intervals. The results are presented as annual averages over 16 years (from 1975 till 1990) and show a gradual increase of the N- and P-concentration in the inlets caused by an intensification of the agriculture in the drainage basin and high domestic sewage releases from the settlements having no waste water treatment. The silicate concentration of the inlets remained constant. Consequently, also a rise of the in-lake concentrations of the two P-fractions was observed. The nitrate concentration of the reservoir Saidenbach increased till 1978, but showed no significant trend over the whole investigation period. The drop of the in-lake silicate concentration during the eighties has to be explained by diminished discharges and, most of all, a higher biological activity as a consequence of the increased P-loading. Intra-annual concentrations calculated as winter, spring, summer (epi- and hypolimnion) and autumn means show the distinct seasonal periodicity of the phosphorus and silicon cycles. Therefore, annual average in-lake concentrations of these nutrients are not quite good measures reflecting changes of the trophic conditions, but rather the winter and early spring values are. No correlations were detected between the annual mean concentrations and the loads. On the other hand, no remarkable seasonal cycling of the nitrate concentrations could be observed and, in this case, a clear dependence exists between annual mean concentrations and loads. The results found for the tributaries of the meso/eutrophic reservoir Saidenbach were compared with those observed in the inlets of the neighbouring oligotrophic reservoir Neunzehnhain. Here the phosphorus concentrations remained almost constant during the time of investigation, but the nitrate concentrations increased too. This must be attributed to agriculture, air pollution and forest management.     

A Class of Distributions in the First Emptiness of a Semi-Infinite Reservoir

This paper considers the probability distribution of the volume of a certain substance (e.g. river discharge, rainfall, deposites of clay, organism, etc.) that flows into a semi-infinite reservoir before its first emptiness for continuous and homogeneous input process when the substance is released at unit rate per unit of time. A few moments of the distribution have been computed. A generalized gamma, and a generalized exponential distributions as particular cases are also discussed. Some possible applications of the generalized negative exponential distribution have been mentioned. These distributions are in fact the continuous analogues of the discrete LAGRANGE distributions recently considered by JAIN and others.     

Calculation of the flow into a lake from underground springs using sedimentation rates

The scope of this work is to quantify the upflows through the underground sources in the bottom of Lake Banyoles (NE-Iberia). The method applied uses the mean settling rate and the fraction of solids per unit of volume of the suspensions at the underground sources, and also the horizontal areas covered by these suspensions. The results obtained reveal that about 90% of the total underground inflow enters the lake through one of the sources. This result agrees with the total underground inflow calculated from the difference of the surface in and outflow of the lake. The behaviour of the suspensions at the underground sources was in a accordance with the theory used to developed the measuring method. Finally, the degree of turbulence in the upper part of the suspension and the importance of the transmissivity of the limestone layer next to the lake are discussed and are found to be negligible.