Combined impact of pesticides and other environmental stressors on taxonomic richness of freshwater animals in irrigation ponds

Rice paddy irrigation ponds can sustain surprisingly high taxonomic richness and make significant contributions to regional biodiversity. We evaluated the impacts of pesticides and other environmental stressors on the taxonomic richness of freshwater animals in 21 irrigation ponds in Japan. We sampled a wide range of freshwater animals (reptiles, amphibians, fishes, mollusks, crustaceans, insects, annelids, bryozoans, and sponges) and surveyed environmental variables related to pesticide contamination, eutrophication, decreased macrophyte coverage, physical habitat destruction, and invasive alien species. Statistical analyses comprised contraction of highly correlated environmental variables, best-subset model selection, stepwise model selection, and permutation tests. Results showed that: (i) probenazole (fungicide) was the unique significant stressor on fish (i.e., contamination with this compound had a significantly negative correlation with fish taxonomic richness), (ii) the interaction of BPMC (insecticide; also known as fenobucarb) and bluegill (invasive alien fish) was a significant stressor on a “large insect” category (Coleoptera, Ephemeroptera, Hemiptera, Lepidoptera, Odonata, and Trichoptera), (iii) the interaction of BPMC and concrete bank was a significant stressor on an “invertebrate” category, (iv) the combined impacts of BPMC and the other stressors on the invertebrate and large insect categories resulted in an estimated mean loss of taxonomic richness by 15% and 77%, respectively, in comparison with a hypothetical pond with preferable conditions.

Temporal variation of water suitability for paddy irrigation needs at karst springs influenced by allogenic recharge in Gunungsewu Karst Area, Indonesia

Irrigation, a critical element in farming, can fulfill crop water needs and increase agricultural productivity during the dry season, provided that the two necessary factors are met, namely water supply and water quality. Water quality is a principal factor in assessing whether or not a water body is usable as a source of irrigation. Excess or lack of elements in irrigation water may affect irrigated crops and soil. For maximum harvests, studies scrutinizing the suitability of water supply for irrigation become necessary. Beton Spring has a large discharge, which the people of Ponjong District, Gunungkidul Regency, rely on for their irrigation and fish farming practices. Uniquely, this karst spring receives allogenic recharges from outside the karst area. This research was intended to assess the suitability of water quality of Beton Spring for temporal irrigation purposes by Sodium analysis (Na%), Sodium Adsorption Ratio (SAR), USSL, and Wilcox. The elements observed in the analysis were Ca2+, Na+, Mg2+, K+ and electrical conductivity. Based on the overall analysis results of the water quality series—Sodium analysis (the water samples were classified as Excellent), SAR (Excellent), USSL (moderate to good), and Wilcox (Excellent to Good), Beton Spring produces good-quality water that is suitable for irrigation.

KENDALI OPTIMAL PERTUMBUHAN POPULASI ECENG GONDOK DENGAN IKAN GRASS CRAP DAN PEMANENAN

Water hyacinth is a wild aquatic plant that grows quickly. The growth of water hyacinth need to be controled to prevent the flood and not to disturb paddy irrigation channels. Grass carp as herbivorous fish is used as natural predator to reduce the population of water hyacinth. The interaction between water hyacinth and grass carp is modeled using the prey-predator system. In this model there are harvest factors and predation factors using Holling type III. The optimal control problem is applied to minimize the mass of water hyacinth and harvest efforts of water hyacinth and maximize the mass of grass carp. The solution uses the Pontryagin Principle. The result is the harvesting of water hyacinth and the grass carp can minimize the water hyacinth biomass at the end of time. Eceng gondok merupakan tanaman liar di perairan yang tumbuh dengan cepat. Pertumbuhannya perlu dikendalikan agar tidak menyebabkan banjir dan tidak mengganggu saluran irigasi persawahan. Ikan grass carp sebagai ikan herbivora digunakan sebagai predator alami untuk mengurangi populasi eceng gondok. Hubungan antara eceng gondok dan ikan grass carp dimodelkan dengan menggunakan sistem prey-predator. Pada model ini terdapat faktor pemanenan dan faktor predasi menggunakan Holling tipe III. Masalah kendali optimal diterapkan dengan tujuan untuk meminimumkan massa eceng gondok dan usaha pemanenan eceng gondok serta memaksimumkan massa ikan grass carp. Penyelesaiannya menggunakan Prinsip Pontryagin. Hasilnya dengan adanya usaha pemanenan eceng gondok dan pengadaan ikan grass carp dapat meminimumkan biomassa eceng gondok di waktu akhir.