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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.

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Seven experimental pilot-scale subsurface vertical-flow constructed wetlands were designed to assess the effect of plants [Typha latifolia L. (cattail)], intermittent artificial aeration and the use of polyhedron hollow polypropylene balls (PHPB) as part of the wetland substrate on nutrient removal from eutrophic Jinhe River water in Tianjin, China. During the entire running period, observations indicated that plants played a negligible role in chemical oxygen demand (COD) removal but significantly enhanced ammonia-nitrogen (NH 4 -N), nitrate-nitrogen (NO 3 -N) total nitrogen (TN), soluble reactive phosphorus (SRP) and total phosphorus (TP) removal. The introduction of intermittent artificial aeration and the presence of PHPB could both improve COD, NH 4 -N, TN, SRP and TP removal. Furthermore, aerated wetlands containing PHPB performed best; the following improvements were noted: 10.38 g COD/ m 2 day, 1.34 g NH 4 -N/m 2 day, 1.04 g TN/m 2 day, 0.07 g SRP/m 2 day and 0.07 g TP/m 2 day removal, if compared to non-aerated wetlands without PHPB being presented.

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