Extreme guanotrophication by phosphorus in contradiction with the productivity of alkaline soda pan ecosystems.

Waterbirds as nutrient vectors can cause high phosphorus loading in shallow inland aquatic ecosystems. The main goal of this study was to determine the causal relationships between the characteristic physico-chemical properties of intermittent (temporary) alkaline soda pan (playa) ecosystems and specific (surface and volume-related) P loading of waterbirds by in situ field investigation, estimation as well as laboratory experiments using standard methods. In addition, our aim was to estimate the contribution of groundwater and precipitation to the total phosphorus pool of soda pans in Hungary. The estimated high specific external P loading of waterbirds (mean: 185 mg P/m2/y, 3.32 mg P/L/year) can explain the majority of the hypertrophic TP pool (mean: 5.17 mg/L, 64%) in soda pans, which is mediated by large-bodied herbivorous (e.g. geese and ducks) and medium-bodied omnivorous (e.g. gulls) waterbirds, who are important external nutrient importers and major phosphorus source. The results also confirm the hypothesis that groundwater (3%) and precipitation (5%) together account for a smaller estimated (8% in this study) contribution to the hypertrophic TP pool in soda pans, while the contribution of waterbirds (64% in this study) to the TP is much higher (64-100%). In this study, the remaining part of TP (maximum 28%) pool can be explained by internal P sources. Soda pans are characterized by physical and chemical characteristics coupled with high densities of waterbirds, as biotic mediators of external P sources, which together cause the maintenance of high concentrations of P-forms. The extreme guanotrophication by high P loading of herbivorous waterbirds causing a hypertrophic state is in contradiction with the limited primary production of natural soda pans. This unique phenomenon can be explained by the multiple impact of prevailing extreme physico-chemical drivers (intermittent hydrological cycle, shallow water depth, high turbidity, salinity, alkalinity) and by the specific nutrient cycle of these alkaline soda ecosystems.

Effect of arsenic-contaminated irrigation water on growth and elemental composition of tomato and cabbage cultivated in three different soils, and related health risk assessment.

This study was carried out to determine the effect of arsenic on tomato and cabbage cultivated in sand, sandy silt, and silt soil, and irrigated with water containing arsenic at concentrations 0.05 and 0.2 mg/L. Increasing arsenic in irrigation water did not affect the photosynthetic machinery. The chlorophyll content index increased in case of all soils and was dependent on the soil nitrogen, phosphorous, and plant biomass. Arsenic concentrations of 0.05 and 0.2 mg/L did not display any phytotoxic symptoms other than reduction in biomass in some cases. In cabbage, arsenic treatment of 0.2 mg/L increased the overall plant biomass production, while in tomato there was a decrease in aerial part and fruit biomass. The biomass production of both plants treated with different concentrations of arsenic, in the three soils was in the following order: silt > sand > sandy silt. Increase of arsenic in the irrigation water resulted in increase in arsenic concentration in the root and aerial part of both plants, at the same cultivation parameters. But tomato fruits displayed a decrease in arsenic accumulation with higher arsenic treatment. In both plants, the arsenic concentration in the plant parts changed in the following order: root > aerial part > fruit. Cabbage accumulated approximately twenty-fold more arsenic in the edible part (0.10-0.25 mg/kg DW) as compared to tomato (0.006-0.011 mg/kg DW) and displayed a good correlation with soil extractable arsenic. When cabbage was cultivated in three different soils applying the same irrigation water, it accumulated arsenic in the following order: sand > sandy silt > silt (p < 0.001 at 0.05 mg/L and p < 0.01 at 0.2 mg/L arsenic treatment). In tomato, the difference in arsenic accumulation among different soil types was highly significant (p < 0.001) but the accumulation pattern varied with the arsenic treatment applied. Sandy soil with the lowest total soil arsenic (4.32 mg/kg) resulted in the highest arsenic concentration in both plants. Among all soils and plants, the transfer factors and bioaccumulation factors were higher in sandy soil, and in cabbage. The estimated daily intake and hazard quotient values for arsenic were lower than 1 in all cases, implying no non-cancerous health risks at the arsenic concentrations applied in our study. Among nutrients only P showed a slight decline with increasing arsenic concentration while all other elements (Mg, K, Ca, S, Si, Fe, Mn, Cu, Zn) did not display any significant changes.