Donghwan Kim

Stream hydrology and water quality are highly interconnected and impacted by climate, land use and geology. We examined this connection using monitoring data from 2000 to 2019 for two streams with contrasting hydrological regimes—intermittent and regulated perennial—in subtropical Queensland, Australia. Our main objective was to evaluate relationships between groundwater levels, climate and flow regulation on the hydrology and water quality of an intermittent and a regulated subtropical stream. In intermittently flowing Lockyer Creek, flow was highly dependent on groundwater levels and occurred when the aquifer was recharged to elevations exceeding the upper 90‐percentile value. With 9.4% of the catchment area in irrigated horticulture, flow in Lockyer Creek was also likely to be reduced by drawdown of the aquifer for irrigation, with no flow for 30% to 81% of days over the observation period for stations in Lockyer Creek. In contrast, flow in the mid‐Brisbane River was continuous, regulated by discharge from a large upstream dam. Nutrient and suspended sediment concentrations in Lockyer Creek were generally higher than in the mid‐Brisbane River, likely associated with runoff from agricultural areas adjacent to the stream, while the upstream dam likely reduced the concentration and variability of nutrients and suspended sediment in the mid‐Brisbane River. During periods of low flow in the mid‐Brisbane River, longitudinal changes in nutrient and suspended sediment concentrations occurred, notably a significant decrease in total and dissolved inorganic nitrogen concentrations downstream (p < 0.05), indicating a possible effect of in‐stream algal uptake and denitrification. This study highlights the impact of human modifications on stream hydrology and water quality in the face of climate change. The findings can inform decision‐making on groundwater irrigation or dam release control for water security.

Stream hydrology and water quality are highly interconnected and impacted by climate, land use and geology. We examined this connection using monitoring data from 2000 to 2019 for two streams with contrasting hydrological regimes – intermittent and regulated perennial – in subtropical Queensland, Australia. Our main objective was to quantify the impact of groundwater level changes and flow regulation on spatio‑temporal patterns in hydrology and water quality in the two streams. In intermittently flowing Lockyer Creek, flow was highly dependent on groundwater levels and occurred when the aquifer was recharged to elevations exceeding the upper 90‑percentile value. With 9.4% of the catchment area in irrigated horticulture, flow in Lockyer Creek was also likely to be reduced by drawdown of the aquifer for irrigation, with no flow for 30% to 81% of days over the observation period for stations in Lockyer Creek. In contrast, flow in the mid‑Brisbane River was continuous, regulated by discharge from a large upstream dam. Nutrient and suspended sediment concentrations in Lockyer Creek were generally higher than in the mid‑Brisbane River, likely associated with runoff from agricultural areas adjacent to the stream, while the upstream dam likely reduced the concentration and variability of nutrients and suspended sediment in the mid‑Brisbane River. During periods of baseflow in the mid‑Brisbane River, longitudinal changes in nutrient and suspended sediment concentrations occurred, notably a significant decrease in total and dissolved inorganic nitrogen downstream (p < 0.05), indicating a possible effect of in-stream algal uptake and denitrification. This study highlights the impact of human modifications on stream hydrology and water quality in the face of climate change. The findings can inform decision-making on groundwater irrigation or dam release control for water security.

Water quality was modeled by a 2-dimensional model (CE-QUAL-W2) in a reservoir (Lake Uiam, Korea) receiving nutrients from both nonpoint sources and point sources. Due to the summer monsoon climate and the aggregated seasonal precipitation pattern, the phosphorus export from nonpoint sources is severely concentrated in the rainy season. For several decades, a sewage treatment plant (STP) on the shore of the lake has been releasing effluent, which was suspected as the major cause of eutrophication. However, the total annual phosphorus loading from the STP was smaller than the loadings from nonpoint sources, which aroused skepticism about the effectiveness of an additional chemical P-removal process in the STP as a eutrophication control strategy. The result of scenario simulations in this study showed that P reduction in the STP effluent from 0.9 mg/L to 0.1 mg/L would effectively reduce the chlorophyll a concentration in the lake by 62%. According to the results of the simulation, the addition of a chemical P-removal process was suggested to the municipal government and was installed in 2012. After the process, the chlorophyll a concentration in the lake decreased as predicted in the simulation. The effect of phosphorus loading can have quite different effects on phytoplankton growth depending on the runoff pattern and hydrological characteristics of the receiving water bodies. Flow rate and nutrient loadings are very dynamic, far from a steady state, in the summer monsoon regions, which may be a unique limnological feature of East Asian countries.