HydroCrowd: a citizen science snapshot to assess the spatial control of nitrogen solutes in surface waters.

We organized a crowdsourcing experiment in the form of a snapshot sampling campaign to assess the spatial distribution of nitrogen solutes, namely, nitrate, ammonium and dissolved organic nitrogen (DON), in German surface waters. In particular, we investigated (i) whether crowdsourcing is a reasonable sampling method in hydrology and (ii) what the effects of population density, soil humus content and arable land were on actual nitrogen solute concentrations and surface water quality. The statistical analyses revealed a significant correlation between nitrate and arable land (0.46), as well as soil humus content (0.37) but a weak correlation with population density (0.12). DON correlations were weak but significant with humus content (0.14) and arable land (0.13). The mean contribution of DON to total dissolved nitrogen was 22%. Samples were classified as water quality class II or above, following the European Water Framework Directive for nitrate and ammonium (53% and 82%, respectively). Crowdsourcing turned out to be a useful method to assess the spatial distribution of stream solutes, as considerable amounts of samples were collected with comparatively little effort.

Relevance of nonfunctional linear polyacrylic acid for the biodegradation of superabsorbent polymer in soils.

Biodegradability is a desired characteristic for synthetic soil amendments. Cross-linked polyacrylic acid (PAA) is a synthetic superabsorbent used to increase the water availability for plant growth in soils. About 4% within products of cross-linked PAA remains as linear polyacrylic acid (PAAlinear). PAAlinear has no superabsorbent function but may contribute to the apparent biodegradation of the overall product. This is the first study that shows specifically the biodegradation of PAAlinear in agricultural soil. Two (13)C-labeled PAAlinear of the average molecular weights of 530, 400, and 219,500 g mol(-1) were incubated in soil. Mineralization of PAAlinear was measured directly as the (13)CO2 efflux from incubation vessels using an automatic system, which is based on (13)C-sensitive wavelength-scanned cavity ring-down spectroscopy. After 149 days, the PAAlinear with the larger average molecular weight and chain length showed about half of the degradation (0.91% of the initial weight) of the smaller PAAlinear (1.85%). The difference in biodegradation was confirmed by the δ(13)C signature of the microbial biomass (δ(13)Cmic), which was significantly enriched in the samples with short PAAlinear (-13‰ against reference Vienna Pee Dee Belemnite,VPDB) as compared to those with long PAAlinear (-16‰ VPDB). In agreement with other polymer studies, the results suggest that the biodegradation of PAAlinear in soil is determined by the average molecular weight and occurs mainly at terminal sites. Most importantly, the study outlines that the size of PAA that escapes cross-linking can have a significant impact on the overall biodegradability of a PAA-based superabsorbent.

Deforestation and benthic indicators: how much vegetation cover is needed to sustain healthy Andean streams?

Deforestation in the tropical Andes is affecting ecological conditions of streams, and determination of how much forest should be retained is a pressing task for conservation, restoration and management strategies. We calculated and analyzed eight benthic metrics (structural, compositional and water quality indices) and a physical-chemical composite index with gradients of vegetation cover to assess the effects of deforestation on macroinvertebrate communities and water quality of 23 streams in southern Ecuadorian Andes. Using a geographical information system (GIS), we quantified vegetation cover at three spatial scales: the entire catchment, the riparian buffer of 30 m width extending the entire stream length, and the local scale defined for a stream reach of 100 m in length and similar buffer width. Macroinvertebrate and water quality metrics had the strongest relationships with vegetation cover at catchment and riparian scales, while vegetation cover did not show any association with the macroinvertebrate metrics at local scale. At catchment scale, the water quality metrics indicate that ecological condition of Andean streams is good when vegetation cover is over 70%. Further, macroinvertebrate community assemblages were more diverse and related in catchments largely covered by native vegetation (>70%). Our results suggest that retaining an important quantity of native vegetation cover within the catchments and a linkage between headwater and riparian forests help to maintain and improve stream biodiversity and water quality in Andean streams affected by deforestation. This research proposes that a strong regulation focused to the management of riparian buffers can be successful when decision making is addressed to conservation/restoration of Andean catchments.

Biodegradability of a polyacrylate superabsorbent in agricultural soil.

Superabsorbent polymers (SAP) are used, inter alia, as soil amendment to increase the water holding capacity of soils. Biodegradability of soil conditioners has become a desired key characteristic to protect soil and groundwater resources. The present study characterized the biodegradability of one acrylate based SAP in four agricultural soils and at three temperatures. Mineralisation was measured as the (13)CO2 efflux from (13)C-labelled SAP in soil incubations. The SAP was either single-labelled in the carboxyl C-atom or triple-labelled including additionally the two C-atoms interlinked in the SAP backbone. The dual labelling allowed estimating the degradation of the polyacrylate main chain. The (13)CO2 efflux from samples was measured using an automated system including wavelength-scanned cavity ring-down spectroscopy. Based on single-labelled SAP, the mean degradation after 24 weeks varied between 0.45% in loamy sand and 0.82% in loam. However, the differences between degradation rates in different soils were not significant due to a large intra-replicate variability. Similarly, mean degradation did not differ significantly between effective temperature regimes of 20° and 30 °C after 12 weeks. Results from the triple-labelled SAP were lower as compared to their single-labelled variant. Detailed results suggest that the polyacrylate main chain degraded in the soils, if at all, at rates of 0.12-0.24 % per 6 months.

Set up of an automatic water quality sampling system in irrigation agriculture.

We have developed a high-resolution automatic sampling system for continuous in situ measurements of stable water isotopic composition and nitrogen solutes along with hydrological information. The system facilitates concurrent monitoring of a large number of water and nutrient fluxes (ground, surface, irrigation and rain water) in irrigated agriculture. For this purpose we couple an automatic sampling system with a Wavelength-Scanned Cavity Ring Down Spectrometry System (WS-CRDS) for stable water isotope analysis (δ2H and δ18O), a reagentless hyperspectral UV photometer (ProPS) for monitoring nitrate content and various water level sensors for hydrometric information. The automatic sampling system consists of different sampling stations equipped with pumps, a switch cabinet for valve and pump control and a computer operating the system. The complete system is operated via internet-based control software, allowing supervision from nearly anywhere. The system is currently set up at the International Rice Research Institute (Los Baños, The Philippines) in a diversified rice growing system to continuously monitor water and nutrient fluxes. Here we present the system's technical set-up and provide initial proof-of-concept with results for the isotopic composition of different water sources and nitrate values from the 2012 dry season.

Trend of herbicide loads in the river Rhine and its tributaries.

Many policies have been established and actions have been taken to reduce pesticide pollution of surface waters. However, the effectiveness of these initiatives was rarely tested on an empirical basis. This study suggests that evidence on the policy effects can be evaluated by analyzing the temporal changes in the loads rather than the concentrations of active ingredients in rivers. It is shown that the long-term change of pesticide emissions into surface waters can be tested statistically by the number of upward versus downward trends in river load. To evaluate the situation in Germany, 57 concentration time series of 14 herbicide substances at 7 river monitoring stations with a minimum of 24 analyses per year were assembled and annual substance river loads were calculated. The longest time course was 17 years (1990-2006). The significance of trends of data rows was analyzed by an univariate Mann-Kendall test that evaluates 27 (47.4%) of the 57 time series as statistically significant downward trended. It took a period of 10 years and longer before the high annual atrazine and simazine loads measured in the years 1990-1991 had been diminished to a drastically lowered level after ban of the herbicides. Data are available on the yearly consumption of 8 substances used in German agriculture. A total of 36 time series for this subset were tested with a partial Mann-Kendall test with the consumption as covariance factor, which reduces the number of significant trends in river load noticeably. Based on this test, only 7 (19.4% of 36) declining time series remain. As a result, the intended effect of measures to reduce surface water contamination by the use of pesticides seems to be only partially successful, however, the database to justify this statement is small. For the water monitoring strategies in Germany, it is recommend to enhance the sampling frequency at river stations. A minimum of a semimonthly sampling interval would facilitate the calculation of valuable annual river loads and would therefore allow a pronounced validation of the long-term change of pesticide emission into rivers.

Biodegradability screening of soil amendments through coupling of wavelength-scanned cavity ring-down spectroscopy to multiple dynamic chambers.

A system was developed for the automatic measurements of ¹³CO2 efflux to determine biodegradation of extra carbon amendments to soils. The system combines wavelength-scanned cavity ring down laser spectroscopy (WS-CRDS) with the open-dynamic chamber (ODC) method. The WS-CRDS instrument and a batch of 24 ODC are coupled via microprocessor-controlled valves. Determination of the biodegradation requires a known δ¹³C value and the applied mass of the carbon compounds, and the biodegradation is calculated based on the ¹³CO2 mixing ratio (ppm) sampled from the headspace of the chambers. The WS-CRDS system provided accurate detection based on parallel samples of three standard gases (¹³CO2 of 2, 11 and 22 ppm) that were measured simultaneously by isotope ratio mass spectrometry (linear regression R² = 0.99). Repeated checking with the same standards showed that the WS-CRDS system showed no drift over seven months.The applicability of the ODC was checked against the closed static chamber (CSC) method using the rapid biodegradation of cane sugar-δ¹³C-labeled through C4 photosynthesis. There was no significant difference between the results from 7-min ODC and 120-min CSC measurements. Further, a test using samples of either cane sugar (C4) or beetroot sugar (C3) mixed into standard soil proved the target functionality of the system, which is to identify the biodegradation of carbon sources with significantly different isotopic signatures.

Mitigation strategies to reduce pesticide inputs into ground- and surface water and their effectiveness; a review.

In this paper, the current knowledge on mitigation strategies to reduce pesticide inputs into surface water and groundwater, and their effectiveness when applied in practice is reviewed. Apart from their effectiveness in reducing pesticide inputs into ground- and surface water, the mitigation measures identified in the literature are evaluated with respect to their practicability. Those measures considered both effective and feasible are recommended for implementing at the farm and catchment scale. Finally, recommendations for modelling are provided using the identified reduction efficiencies. Roughly 180 publications directly dealing with or being somehow related to mitigation of pesticide inputs into water bodies were examined. The effectiveness of grassed buffer strips located at the lower edges of fields has been demonstrated. However, this effectiveness is very variable, and the variability cannot be explained by strip width alone. Riparian buffer strips are most probably much less effective than edge-of-field buffer strips in reducing pesticide runoff and erosion inputs into surface waters. Constructed wetlands are promising tools for mitigating pesticide inputs via runoff/erosion and drift into surface waters, but their effectiveness still has to be demonstrated for weakly and moderately sorbing compounds. Subsurface drains are an effective mitigation measure for pesticide runoff losses from slowly permeable soils with frequent waterlogging. For the pathways drainage and leaching, the only feasible mitigation measures are application rate reduction, product substitution and shift of the application date. There are many possible effective measures of spray drift reduction. While sufficient knowledge exists for suggesting default values for the efficiency of single drift mitigation measures, little information exists on the effect of the drift reduction efficiency of combinations of measures. More research on possible interactions between different drift mitigation measures and the resulting overall drift reduction efficiency is therefore indicated. Point-source inputs can be mitigated against by increasing awareness of the farmers with regard to pesticide handling and application, and encouraging them to implement loss-reducing measures of "best management practice". In catchments dominated by diffuse inputs at least in some years, mitigation of point-source inputs alone may not be sufficient to reduce pesticide loads/concentrations in water bodies to an acceptable level.

Point- and nonpoint-source pesticide contamination in the Zwester Ohm catchment, Germany.

Reducing pesticide loads in surface waters implies identifying the pathways responsible for the pollution. The current study documents the pesticide contamination of the river Zwester Ohm, a 4917-ha catchment in Germany with 41% of the land used for crop production. Discharges and concentrations of 19 pesticides were measured continuously at three locations for 15 mo. The load detected at the outlet of the catchment amounted to 9048 g a.i. The losses represent 0.22% of the pesticides applied by the farmers. The contamination showed a seasonal pattern following the pesticide application times. The wastewater treatment plant system (WWTPS) in the catchment (two wastewater treatment plants [WWTP], 14 combined sewer overflows (CSO), four CSO tanks) emits during dry weather periods purified sewage and during storm events sewage mixed with stormwater runoff into the river. The contribution by the WWTPS to the pesticide load was defined as point-source pollution (PSP). The load was dominated by PSP with at least 77% of the total pollution. No significant interdependencies between intrinsic properties of the pesticides, hydrometeorological factors, and the loads occurring in the stream could be found. Therefore, it is not possible to predict PSP for other catchments based on the results from this study. Whereas 65% of the total load entered the river via the WWTP, a portion of 12% was attributed to the CSO. The study points out that the influence of CSO on PSP should be taken into account in future catchment studies in areas with comparable agricultural structure.