Eutrophication in aquaculture ponds is one of the major issues related to both the environment and the health of consumers. This study has selected and conducted a water-quality survey of nine freshwater aquaculture ponds in Ho Chi Minh City. The empirical results showed that these ponds were seriously polluted with COD and BOD5 whose values did not meet the B2 column of the Vietnamese National Technical Regulation on Surface Water Quality (QCVN 08-MT:2015/BTNMT). On the other hand, most N-NH4+ and N-NO2- concentrations in the ponds met the threshold value of B2 column. The values of the chlorophyll-a are greater than 10 μg/L, indicating that investigated ponds are in a state of eutrophication. In addition, the results of the TSI calculations showed that most of the sites that are in hypereutrophication state and phosphorus is identified as the eutrophication limit factor in these sites. / Phú dưỡng hóa nguồn nước nuôi trồng thủy sản là một trong các vấn đề lớn liên quan đến cả môi trường và sức khỏe người tiêu dùng. Nghiên cứu này đã lựa chọn và tiến hành khảo sát chất lượng nước của chín ao hồ nuôi thủy sản trên địa bàn thành phố Hồ Chí Minh. Kết quả phân tích cho thấy các ao hồ trên bị ô nhiễm hữu cơ nặng với thông số COD và BOD5 đều không đạt chuẩn B2 theo quy chuẩn kỹ thuật quốc gia về chất lượng nước mặt (QCVN 08-MT:2015/BTNMT). Về mặt ô nhiễm các chất dinh dưỡng, nồng độ N-NH4+ và N-NO2- đa số chỉ thỏa mãn loại B2, thậm chí vượt ngưỡng quy định của cột B2. Các giá trị của thông số chlorophyll-a đều lớn hơn 10 μg/L, chứng tỏ các ao hồ khảo sát đều đang trong tình trạng phú dưỡng. Thêm vào đó, kết quả tính toán chỉ số TSI cho thấy hầu hết các vị trí nghiên cứu đang ở trạng thái siêu phú dưỡng và photpho được xác định là yếu tố giới hạn sự phú dưỡng của các vị trí khảo sát nêu trên.

Coleanthus subtilis ist eine durch die FFH-Richtlinie geschützte, weltweit sehr seltene Art, welche periodisch trockenfallende Standorte in Flussauen (Primärhabitate) bzw. durch den Menschen geschaffene Staugewässer (Sekundärhabitate) besiedelt. Die Erarbeitung der aktuellen Verbreitungsbilder der Art in Sachsen und ihrer Besiedlungshistorie waren Ausgangspunkt für die Analysen zur Ökologie dieser Art. Anhand von Analysen zu den Ausbreitungsmechanismen, Standortansprüchen und Reaktionsmöglichkeiten von C. subtilis wurden grundlegende Beiträge zum besseren Verständnis der Strategien dieser Art erbracht. Die Arbeit gibt Hinweise für eine artenschutzgerechte Bewirtschaftung der Staugewässer insbesondere für die Regulierung von Zeitpunkt, Dauer, Intensität und Häufigkeit von Wasserstandsabsenkungen sowie hinsichtlich einzelner Praktiken im Zusammenhang mit einer fischereilichen Nutzung. Weiterhin zeigt die Arbeit auf, wie C. subtilis auf bestimmte, von den durchschnittlichen Wasserstandsschwankungen abweichende, Bedingungen reagieren kann. Damit sind nun wichtige Grundlagen zum nachhaltigen Schutz und zur Förderung von C. subtilis, insbesondere in Sekundärhabitaten, vorhanden. / Coleanthus subtilis is a globally rare species protected by the European Union Habitats Directive. This grass establishes on periodically drying sites in river floodplains (primary habitats) but also in man made ponds and reservoirs (secondary habitats). The identification of the present distribution patterns as well as the reconstruction of the colonisation history of C. subtilis in Saxony were the basis for analyses about the ecology of this species. By analysing dispersal mechanisms, habitat demands and response traits of C. subtilis fundamental contributions to a better understanding of the strategies of this species are given. The thesis provides information about optimum time, duration, intensity and frequency of water level reductions and about the consequences of different management practices particularly with respect to fishery in ponds and reservoirs inhabiting C. subtilis. Further the thesis shows how C. subtilis can cope with deviations from mean water level fluctuations. In summary important fundamental knowledge for the sustainable conservation and promotion of C. subtilis, particularly in secondary habitats, has been established.

Coleanthus subtilis ist eine durch die FFH-Richtlinie geschützte, weltweit sehr seltene Art, welche periodisch trockenfallende Standorte in Flussauen (Primärhabitate) bzw. durch den Menschen geschaffene Staugewässer (Sekundärhabitate) besiedelt. Die Erarbeitung der aktuellen Verbreitungsbilder der Art in Sachsen und ihrer Besiedlungshistorie waren Ausgangspunkt für die Analysen zur Ökologie dieser Art. Anhand von Analysen zu den Ausbreitungsmechanismen, Standortansprüchen und Reaktionsmöglichkeiten von C. subtilis wurden grundlegende Beiträge zum besseren Verständnis der Strategien dieser Art erbracht. Die Arbeit gibt Hinweise für eine artenschutzgerechte Bewirtschaftung der Staugewässer insbesondere für die Regulierung von Zeitpunkt, Dauer, Intensität und Häufigkeit von Wasserstandsabsenkungen sowie hinsichtlich einzelner Praktiken im Zusammenhang mit einer fischereilichen Nutzung. Weiterhin zeigt die Arbeit auf, wie C. subtilis auf bestimmte, von den durchschnittlichen Wasserstandsschwankungen abweichende, Bedingungen reagieren kann. Damit sind nun wichtige Grundlagen zum nachhaltigen Schutz und zur Förderung von C. subtilis, insbesondere in Sekundärhabitaten, vorhanden. / Coleanthus subtilis is a globally rare species protected by the European Union Habitats Directive. This grass establishes on periodically drying sites in river floodplains (primary habitats) but also in man made ponds and reservoirs (secondary habitats). The identification of the present distribution patterns as well as the reconstruction of the colonisation history of C. subtilis in Saxony were the basis for analyses about the ecology of this species. By analysing dispersal mechanisms, habitat demands and response traits of C. subtilis fundamental contributions to a better understanding of the strategies of this species are given. The thesis provides information about optimum time, duration, intensity and frequency of water level reductions and about the consequences of different management practices particularly with respect to fishery in ponds and reservoirs inhabiting C. subtilis. Further the thesis shows how C. subtilis can cope with deviations from mean water level fluctuations. In summary important fundamental knowledge for the sustainable conservation and promotion of C. subtilis, particularly in secondary habitats, has been established.