Many lakes and rivers are enriched with high levels of suspended sediments (SPS). Denitrification occurring on suspended sediments (DSS) may play an important role in nitrogen removal in water columns with high SPS concentrations. Poyang Lake, with dramatic hydrologic variations, has high spatial and seasonal variation of SPS, and we hypothesized that DSS and nitrogen removal in this lake would vary similarly. DSS in Poyang Lake was determined by the traditional acetylene-inhibition method combined with a batch mode assay. Laboratory simulation experiments were also conducted to examine the factors controlling denitrification occurring on SPS. Seasonally, DSS rates at 15 sampling sites in Poyang Lake were 0.63 ± 0.24, 0.29 ± 0.17, 0.25 ± 0.18, and 0.52 ± 0.37 μmol N·L−1·d−1, respectively in spring, summer, autumn, and winter. Spatially, average DSS rates were higher in the northern lake area, which is connected to the Yangtze River, than in the upstream and central lake area. Lowest DSS rates occurred in semi-closed bay and dish lakes. Spatial and seasonal variations of DSS rates were affected by a combination of factors, in which nitrate concentrations, SPS composition, and concentrations of organic-SPS were the most important. These influencing factors were seasonally dependent, with nitrate concentrations having stronger effects on DSS during wet seasons than dry seasons. Results from a multiple stepwise regression model also demonstrated that DSS tended to occur on fine particles (e.g., clay particles, <4 μm). Evaluation of annual nitrogen loss by DSS was estimated according to the seasonal water budget and DSS rates in Poyang Lake. The total nitrogen loss by DSS was estimated to be 10800 ± 6090 t, which accounted for 2.8–9.9% of the nitrogen input, and this proportion was comparable to nitrogen removal by sediment denitrification. This result confirms that DSS was an important nitrogen sink in this large, turbid lake.

In this study water balance components as well as nitrogen and dissolved organic carbon leaching were quantified by means of large weighable grassland lysimeters at three sites (860, 770 and 600 m a.s.l.) for both intensive and extensive management. Our results show that at E600, the site with highest air temperature (8.6 °C) and lowest precipitation (981.9 mm), evapotranspiration losses were 100.7 mm higher as at the site (E860) with lowest mean annual air temperature (6.5 °C) and highest precipitation (1359.3 mm). Seepage water formation was substantially lower at E600 (−440.9 mm) as compared to E860. Compared to climate, impacts of management on water balance components were negligible. However, intensive management significantly increased total nitrogen leaching rates across sites as compared to extensive management from 2.6 kg N ha−1 year−1 (range: 0.5–6.0 kg N ha−1 year−1) to 4.8 kg N ha−1 year−1 (range: 0.9–12.9 kg N ha−1 year−1). N leaching losses were dominated by nitrate (64.7%) and less by ammonium (14.6%) and DON (20.7%). The low rates of N leaching (0.8–6.9% of total applied N) suggest a highly efficient nitrogen uptake by plants as measured by plant total N content at harvest. Moreover, plant uptake was often exceeding slurry application rates, suggesting further supply of N due to soil organic matter decomposition. The low risk of nitrate losses via leaching and surface runoff of cut grassland on non-sandy soils with vigorous grass growth may call for a careful site and region specific re-evaluation of fixed limits of N fertilization rates as defined by e.g. the German Fertilizer Ordinance following requirements set by the European Water Framework and Nitrates Directive.

The forest hydrologic budget may be impacted by increasing CO2 and tropospheric O3. Efficient means to quantify such effects are beneficial. We hypothesized that changes in the balance of canopy interception, stem flow, and through-fall in the presence of elevated CO2 and O3 could be discerned using image analysis of leafless branches. We compared annual stem flow to the results of a computerized analysis of all branches from the 2002, 2004, and 2006 annual growth whorls of 97 ten-year-old trees from the Aspen Free-Air CO2 and O3 Enrichment (Aspen FACE) experiment in Rhinelander, WI. We found significant effects of elevated CO2 and O3 on some branch metrics, and that the branch metrics were useful for predicting stem flow from birch, but not aspen. The results of this study should contribute to development of techniques for efficient characterization of effects on the forest hydrologic budget of increasing CO2 and tropospheric O3. Canopy architecture and stem flow are affected by elevated CO2 and tropospheric O3.

The formation of evaporites associated with the final stages of the precipitation sequence, such as the case of halite, is frequent in marshes in arid areas, but it is not to be expected in those humid climates. This work, by means of the study of the hydrological, climatic and land use conditions, identifies the factors that allow the formation of saline precipitations in a marsh located in a humid climate area. The results obtained show that the exclusion of the marsh as a result of the embankment is the main reason for the presence of halite. It is to be expected that in the future the growth of the embanked marsh areas, together with the climatic and tidal condition tendencies recorded, will favour a higher rate of formation of evaporite salts. The identification of these factors makes it possible to set basic sustainable management guidelines to avoid soil salinisation.

Although recent studies show that the iron oxides do not enter or accumulate in plants, they may preclude the transport of water and nutrients in the plants through/as a consequence of their aggregation on the surface of the roots. The feasibility of using iron oxide nanoparticles to modify the availability of trace elements (TEs) to Helianthus annuus in the soil as well as their interference with the plant response during an imposed water deficiency stress were studied in a pot experiment. Plants were grown in a compost pre-amended contaminated soil with and without nano-maghemite (NM) and later exposed to drought. The nano-amendment promoted the growth of H. annuus (higher (25 %) dry weight than in the same soil without NM), mainly due to the insolubilisation of pore water Zn in the soil and the consequent reduction of its availability to the plants. During the water stress, NM did not cause an increase in the accumulation of proline or total amino acids in the plants, which are normally used as drought stress indicators, compared to the control plants without NM. In conclusion, NM could be useful soil amendments during phytoremediation procedures, since it can immobilise TEs in the soil without disrupting the plant water balance.

Phosphorous dynamics within Lake Sirio (NW Italy) were investigated, considering both water and sediments. The total phosphorus (TP) concentration in the water is about 79 μg l-¹ after the winter mixing, that is in homogeneous conditions; then TP content increases up to an average of 360 μg l-¹ in late autumn in the deep hypolimnium (30-45 m). This deep lake portion accounts for only 1/12 of the water volume. Close to the water-sediment interface, TP concentrations up to 530 μg l-¹ are observed. Sediment sampled at depths of 20 and 33 m contains less than 2,000 mg kg-¹ of TP, whereas cores from the deepest sediments (46 m) display TP values of 2,000-4,000 mg kg-¹ at the water-sediment interface, increasing with depth to 16,000 mg kg-¹ at about 60-100 cm. In these deep sediments the main chemical form is the Al-Fe-Mn bound P (about 90% in the high TP cores) and Fe and Mn are also highly enriched (3 and 9 times more than in the shallow sediments respectively). The P-Fe association is confirmed by SEM-EDS and XRD analyses. The vertical distribution of the P content in the water column is consistent with its release from sediments, but in this hypothesis an unrealistic P release rate from 8.1 to 3.0 g m-²y-¹ was estimated. A more complex model is therefore proposed, involving a process of P concentration in the sediments of the central (deepest) part of the lake, and a short term sediment-water exchange. The TP vertical variability and speciation in the cores suggests a change in the sediment retention capacity, connected to the lake shift to more eutrophic conditions.

Field study at the Cervenohorske sedlo (1,013 m a.s.l.) (Hruby Jesenik Mountains, the Czech Republic, Central Europe) during 1999-2002 has been conducted in order to analyse the chemistry of rain/snow water using bulk and throughfall collector and fog/cloud water using modified passive Grunow collector. Fog water input to coniferous forest (Picea abies) was quantified using canopy balance method. For all samples pH, and the concentrations of [graphic removed] , Ca²⁺, K⁺, Mg²⁺, Na⁺, Cl-, [graphic removed] , and [graphic removed] were measured. The volume-weighted mean pH value varied from 4.92 to 5.43 in open bulk precipitation, from 4.30 to 4.71 in throughfall and from 4.66 to 5.23 in fog water. The fog droplets generally contain higher ion concentrations than rainwater. The related enrichment factors lie between 1.1 and 10.7 for the relevant species. The fog samples exhibit higher concentrations of [graphic removed] and [graphic removed] as compared to the bulk samples during 2000-2002. [graphic removed] are 5.7-10.7 times more concentrated in fog water and [graphic removed] are 3.4-7.2 times more concentrated in fog water. These differences may result from the height and characteristics of formation of the droplets. Based on canopy balance method, the annual fog water inputs were estimated to be 22 and 19% of rain and snow annual amounts in 1999 and 2000, respectively. For [graphic removed] , [graphic removed] , and [graphic removed] , the contribution of fog deposition in total (bulk + fog) deposition is estimated as 54, 47, and 42%, respectively.

This study aimed to quantify the water balance components at a grassland and a forest site representative of the Atlantic Forest biome in southern Brazil using drainage lysimeters. Since it was not possible to place mature trees on the forest lysimeter, it was planted with young trees and understory vegetation. Data from this lysimeter and computations with the water balance and the Penman-Monteith equation were then used to assess the values of the water balance components for the mature forest.Total precipitation during the study period was 2308 mm. In the forest environment, 46% thereof was intercepted by the canopy from where it later evaporated. Hence, much less rain reached the ground than under grassland. Runoff from both sites was <1% of precipitation and therefore not a significant factor in the water balance. Cumulative drainage amounted to 1136 mm from grassland: from the mature forest, it was estimated to be 389 mm. There were two reasons for this low value under forest: Interception prevented a lot of water from reaching the ground, and the actual evapotranspiration from the mature forest was much higher than from grassland (1231 mm compared to 1964 mm).