Sensitivity Analysis in Linear Regression

Anthropogenic influences on the water quality of the Baiyangdian Lake in North China over the last decade.

The problem of managing water scarcity by resorting to complex interconnected multi-source water systems needs to utilize management optimization techniques analyzing aspects of water quantity and quality in a common strategy. In the southern regions of Mediterranean Europe, the greater part of water resources for supply systems are derived from artificial reservoirs and water systems can become quite complex since they interconnect several sources and demand centers, as indeed occurs in the Region of Sardinia (Italy). A simplified approach to the requirement to insert water quality aspects in the mathematical optimization model can be achieved by examining the trophic conditions of reservoirs. Trophic State Indexes (TSI) based on Carlson’s (1977) make it possible to insert quality constraints in the water management optimization model also considering complex multi-reservoir and multi-user systems. Model formalization and implementation by the optimization toolkit WARGI (Water Resource system optimization aided by Graphical Interface) (Sechi and Zuddas 2000; Manca et al. 2004; Salis et al. 2005) is illustrated in this paper. The usefulness of a mixed quantity–quality optimization approach has been confirmed by WARGI application to a real multi-reservoir water resources system in southern Sardinia. The optimization model remains computationally efficient dealing with this complex multi-reservoir system and the obtained results can be seen as a reference target in a subsequent simulation phase.

Multi-Reservoir System Optimization Using Chlorophyll-a Trophic indexes

Occurrence of water phosphorus at the water-sediment interface of a freshwater shallow lake: Indications of lake chemistry

The organic carbon, permeability test, grain size, chemical composition, and mineral composition were analyzed for 147 samples collected from the Luan River catchment, Hebei province, China, to quantitatively characterize the effects of land use, climate change, sedimentary environment, mineral composition, and chemical composition on the spatial and temporal variation of soil organic carbon (SOC). The results indicate that there was higher SOC content and stronger variation in the south plain than in the northern low mountain. The effects of land use, climate change, and sedimentary environment on SOC distribution were greater than the effects of mineral composition and chemical composition. The cropping systems in the Luan River catchment resulted in significant difference in SOC concentration between the south plain and north mountain. The precipitation mainly transmitted its effects through the sedimentary environment to SOC, which caused the stronger temporal variation in SOC from June to October in the south plain. The north mountain did not have significant temporal variation because of the lower hydraulic conductivity of the sedimentary sequence. The spatial variation of SOC was correlated with land use, and their temporal variation was attributed to climate change and sedimentary environment. Apart from land use, the decision maker can also affect the organic carbon mineral and sequence through the sedimentary environment.

Spatial and temporal variation of soil organic carbon in the North China Plain

Efficacy of phosphorus (P) mitigation strategies in lake basins could not be quantitatively evaluated due to a lack of assessment frameworks, confounding preferential management. The promiscuity in contributions of P sources to burden is a major cause. This study aimed to spatially profile water P burden with special emphasis on assessing dominance of P sources in a lake system. Exploratory data analysis with multivariate statistical techniques was applied to interpret raw data matrix of 21 variables employed in water and sediment samples collected from Baiyangdian Lake, the largest freshwater shallow lake in North China. Simple trend surface analysis was performed to estimate P distribution similarities. Multivariate exploratory analysis was conducted on variables and sites to accomplish pattern recognition and magnitude identification of sources. Linear regression model was applied to quantitatively determine importance of P regulators. Results revealed that P fractionation in sediments reflected the dominance of P sources and played a pivotal role in discriminating water P burden. Intensive P enrichment was highly associated with nitrogen levels and conductivity as response of exogenous input. Sedimentary sand fraction needed more concern due to its high risks of potential sink and preferential release. Metallic oxide bound P along with organic P served as main sediment contributions. Pertinent separate strategies were suggested to be implemented sub-regionally in mitigating effects of P downstream. The proposed framework enabled assessment on source-related P burden to evaluate profits of P reduction management options and provided an alternative framework of focal point determination for local government agencies.

Spatial Profiling and Assessing Dominance of Sources to Water Phosphorus Burden in a Shallow Lake

Knowledge is limited on soil organic carbon (SOC) and total nitrogen (TN) dynamics shaped by seasonal freezing-thawing cycles under long-term conventional cultivation. This study aimed to elaborate temporal variability of SOC and TN in the plow layer of agricultural soils employing a dataset of a long-term observation (1965–2010). Cumulative losses were calculated via mass balance equation. With the aid of the autoregression integrated moving average model (ARIMA), time series of historical and impending variations of SOC and TN levels were simulated and depicted. Results revealed that SOC and TN contents decreased by 15 and 42 %, respectively. Annual nutrient variations exhibited deteriorating tendencies with fluctuations ranging within −745 and 759 kg C ha−1 year−1 and −432 and 35 kg N ha−1 year−1, respectively. SOC presence was strictly regulated by N input following a regional pattern. Chemical fertilization, combined with crop residue compost, boosted SOC and TN enrichment, but raised the loss risks. Involvement of green manure/fallow treatment with 1-year frequency in crop rotations favored SOC and TN sequestration. Paddy management was beneficial for SOC accumulation. ARIMA modeling demonstrated annual release rates of 468 kg C ha−1 for SOC and 214 kg N ha−1 for TN in subsequent 10 years. The generated algorithms provided a tool to estimate regional SOC and TN losses following cultivation, and to evaluate soil fertility.

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Temporal Trends of Soil Organic Carbon and Total Nitrogen Losses in Seasonally Frozen Zones of Northeast China: Responses to Long-Term Conventional Cultivation (1965–2010)

Jing Xie

Papers

Spatial Profiling and Assessing Dominance of Sources to Water Phosphorus Burden in a Shallow Lake

Temporal Trends of Soil Organic Carbon and Total Nitrogen Losses in Seasonally Frozen Zones of Northeast China: Responses to Long-Term Conventional Cultivation (1965–2010)