Decadal change in tripton concentration in a shallow lake

Abstract

In shallow polymictic lakes where the resuspension of sediments frequently occurs, tripton (non-living particulate materials) can affect physical, chemical and biological processes. Over the last four decades, substantial changes in tripton concentrations and therefore limnological parameters have been observed in Lake Kasumigaura, a shallow eutrophic lake.To build a conceptual model of the various relationships between these, we analyzed data on monthly water and yearly sediment quality at several stations together with meteorological information. Large short-term and decadal variations were characteristics for tripton. Annual averages in tripton concentration changed substantially (e.g., from 3 to 25 mg l −1 at the lake center), peaking in the early 2000s, when phosphorus and silicon in water were high, and we observed a large proportion of diatoms in phytoplankton and low light penetration. Tripton concentration showed a positive correlation with sediment water content (WC) and a negative one with sediment ignition loss (IL) with a few years' delay, confirming the results of previous hydraulic experiments. Using these parameters, multiple regression models for estimating tripton concentrations were constructed and showed good performances (e.g., adjusted r 2 = 0.61 at the center). Furthermore, changes in inorganic ions in water, probably resulting from meteorological variations, were inferred to bring about changes in sediment WC. On the other hand, the amount of Microcystis sp. in water was suspected to govern the sediment IL. We reveal many processes (physical, chemical, biological and meteorological phenomena) related to tripton, and thus, their relationships could be considered a conceptual model for a shallow lake.

Long-term changes in water mineral concentrations and their influence on sediment water content in a shallow lake

“…Over the last four decades, substantial changes in tripton concentrations have been observed in Lake Kasumigaura, a shallow eutrophic lake. Tripton concentration showed a positive correlation with sediment water content (WC) and a negative one with sediment ignition loss (IL) with a few years' delay [3]. Results of hydraulic experiments with sediment samples [4] were in agreement.…”

“…Such organisms included in SS in the experiment would be died by the elevated salt concentration and SS concentration was decreased. However, based on the finding that the direct influence of changes in mineral concentrations on the tripton trend was not of major importance (insignificant correlations between tripton and major ions [3]), we would conclude that the indirect influence through sediment WC change was influential on suspended particle concentrations in Lake Kasumigaura as shown in Introduction [3,4]. That is, tripton concentration in this lake is mainly governed not by settling process, but by resuspension process.…”

“…Of the 50 water quality parameters recorded in the KRO database as explained in Fukushima et al [3], the focus in this study was on major inorganic cations and anions (sodium [Na + ], potassium [K + ], magnesium [Mg 2+ ], calcium [Ca 2+ ], chloride [Cl − ], and sulphate [SO 4…”

“…In Lake Kasumigaura, sediment resuspension is principally caused by wind wave [18]. The magnitude of wind wave is determined by wind fetch and velocity, but there were not clear decadal changes in wind velocity (e.g., yearly maximum wind velocity, number of days when daily maximum wind velocity was larger than 10 m s −1 ; [3]). Third, the sediment WC and porosity monotonously decreased from the surface to the depth of more than 40 cm [20], indicating relatively stable sedimentation processes.…”

“…In order to help to solve the above-mentioned questions, the purposes of the present study are (1) to clarify the long-term changes in mineral ions and sediment properties by analyzing 38 years of data obtained in Lake Kasumigaura, a shallow eutrophic lake, and determine their relationships; (2) to determine experimentally the relationships of mineral ion concentrations with sediment water content and turbidity in overlying water as indicated by the field data; and (3) to analyze the reasons for the changes in mineral ions in the lake. Thus, we think that the innovation of this study is to elucidate the relationship between lake salinity and sediment water content based on the analysis on long-term monitoring data and laboratory experiments.…”