The relationships between pH, dissolved oxygen (DO) and chlorophyll a in aquaculture and non-aquaculture waters are assessed in this paper. The research includes the evaluation of field and experimental studies at the Panjiakou Reservoir (between Aug and Oct 2009) and the review of international data covering two decades. The results indicated that typical eutrophic non-aquaculture water had mean concentrations of chlorophyll a of higher than 10 μg L −1 , and significant positive correlations were found between pH, DO and chlorophyll a. When the mean concentration of chlorophyll a was less than 10 μg L −1 , no correlation was found between DO and chlorophyll a for waters with a high exchange rate or heavily organically polluted natural waters. Diurnal variations were found for both pH and DO. A corresponding significant positive correlation was found between both water quality parameters. In general, when the mean concentration of chlorophyll a was less than 10 μg L −1 within aquaculture waters of low exchange rate, only a weak or no correlation at all was found between pH, DO and chlorophyll a during summer and autumn. On the other hand, a significant positive correlation between pH and chlorophyll a and a significant positive correlation or no correlation between DO and chlorophyll a were found for aquaculture waters with a high exchange rate during summer and autumn. Strong diurnal variations for both pH and DO were identified. A significant positive linear correlation between pH and DO was found for field enclosure experiments.

The impact of hydraulic loading rate (HLR) and seasonal temperature on contaminant removal efficiencies within an integrated constructed wetland (ICW) system of 3.25 ha was assessed. The ICW system was designed to treat domestic wastewater from Glaslough (Ireland). The current loading rate is 800 population equivalents. The system has shown good removal performances (2008 to 2010). Mean concentration removal efficiencies were high: 92% for chemical oxygen demand (COD), 98% for the 5 days at 20°CN-allylthiourea biochemical oxygen demand (BOD), 94% for total suspended solids (TSS), 97% for ammonia-nitrogen (NH 3 -N), 90% for nitrate-nitrogen (NO 3 -N), 96% for total nitrogen (TN), and 96% for molybdate reactive phosphate (MRP). The mean mass removal efficiencies were 92% for COD, 98% for BOD, 96% for TSS, 92% for NH 3 -N, 83% for NO 3 -N, 90% for TN, and 91% for MRP. Loading rate fluctuations were mainly due to high variation in rainfall (0.4 to 400 m 3 day -1 ) and in evapotranspiration rate (0 to 262 m 3 day -1 ). The influence on the removal efficiencies of the hydraulic loading rate (−0.7 to 15.3 cm day -1 ), which was based on overall water balance, was negligible. This implies that the large footprint of the system provides a high hydraulic retention time (92 days).

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Constructed wetland sediments are frequently contaminated with nitrogen and phosphorus. There is a risk that accumulated pollutants can either be remobilised or reach the groundwater. Five identical mesocosms, which were filled with subsoil collected from full‐scale integrated constructed wetland (the first cell receives the most contaminated influent), were set up to examine nutrient removal within sediment layers. The results indicated that accumulated nutrients leached out into inflow water and that the sediment capacity of nutrient retention decreased as the wetlands aged. Furthermore, the mesocosm planted with Phragmites australis achieved better treatment results compared with the one planted with Agrostis stolonifera. The risk of contamination to groundwater does not exist because none of the treated water reached the bottom outlet during the study period. Both the bentonite (clay) and biogeochemical processes taking place within sediments proved to be efficient in preventing polluted water from infiltrating into lower lying soils.