High‐Frequency Dissolved Organic Carbon and Nitrate Measurements Reveal Differences in Storm Hysteresis and Loading in Relation to Land Cover and Seasonality

Storm events dominate riverine loads of dissolved organic carbon (DOC) and nitrate and are expected to increase in frequency and intensity in many regions due to climate change. We deployed three high‐frequency (15 min) in situ absorbance spectrophotometers to monitor DOC and nitrate concentration for 126 storms in three watersheds with agricultural, urban, and forested land use/land cover. We examined intrastorm hysteresis and the influences of seasonality, storm size, and dominant land use/land cover on storm DOC and nitrate loads. DOC hysteresis was generally anticlockwise at all sites, indicating distal and plentiful sources for all three streams despite varied DOC character and sources. Nitrate hysteresis was generally clockwise for urban and forested sites, but anticlockwise for the agricultural site, indicating an exhaustible, proximal source of nitrate in the urban and forested sites, and more distal and plentiful sources of nitrate in the agricultural site. The agricultural site had significantly higher storm nitrate yield per water yield and higher storm DOC yield per water yield than the urban or forested sites. Seasonal effects were important for storm nitrate yield in all three watersheds and farm management practices likely caused complex interactions with seasonality at the agricultural site. Hysteresis indices did not improve predictions of storm nitrate yields at any site. We discuss key lessons from using high‐frequency in situ optical sensors

Peak grain forecasts for the US High Plains amid withering waters

ACKNOWLEDGMENTS. This paper stems from discussions during the Ettersburg Ecohydrology Workshop in Germany (October 2018), with the corresponding manuscript preparation ensuing in subsequent months. The workshop was funded by the UNIDEL Foundation, Inc. and the University of Delaware. Accordingly, partial support for this paper derived from funding for the workshop. A.M. was supported by the US NSF (Grants NSF-AGS-1644382 and NSF-IOS-175489).Peer reviewedPublisher PD

Evaluation of metals that are potentially toxic to agricultural surface soils, using statistical analysis, in northwestern Saudi Arabia

© 2015, Springer-Verlag Berlin Heidelberg. Heavy metals in agricultural soils enter the food chain when taken up by plants. The main purpose of this work is to determine metal contamination in agricultural farms in northwestern Saudi Arabia. Fifty surface soil samples were collected from agricultural areas. The study focuses on the geochemical behavior of As, Cd, Co, Cr, Cu, Hg, Pb and Zn, and determines the enrichment factor and geoaccumulation index. Multivariate statistical analysis, including principle component analysis and cluster analysis, is also applied to the acquired data. The study shows considerable variation in the concentrations of the analyzed metals in the studied soil samples. This variation in concentration is attributed to the intensity of agricultural activities and, possibly, to nearby fossil fuel combustion activities, as well as to traffic flows from highways and local roads. Multivariate analysis suggests that As, Cd, Hg and Pb are associated with anthropogenic activities, whereas Co, Cr, Cu and Zn are mainly controlled by geogenic activities. Hg and Pb show the maximum concentration in the analyzed samples as compared to the background concentration

AN IN SITU METHOD TO MEASURE AND MAP BARK PH

Bark pH is an essential parameter which partly governs the chemistry of the bark as well as its suitability as a microhabitat to a wide range of epiphytic organisms. Bark pH is known to vary with tree species, epiphytic cover, stemflow channelization, and anthropogenic influences. To date, reliable methods to quantify the spatial and temporal dimensions of bark pH have remained elusive. The aim of the present study was to develop and validate an in situ method to measure the surface pH of bark with high spatial resolution. Agar-agar panels, prepared with a pH indicator, were used to quantify and map the spatial variation of bark pH for cacao trees in Indonesia. Fine-scale changes of bark pH were clearly detectable and quantifiable with our bark pH mapping method. Bark pH was found to vary as a function of bark microrelief and the presence of epiphytes. The use of pH reference panels validated the bark pH measurements obtained from our method. The bark pH measurement method developed, described, and validated in this article is inexpensive and straightforward. It has the potential for wide adoption by scientists across disciplines who are interested in bark pH and its effect on life in the cortisphere. Unlike conventional methods to measure bark pH in deionized water or KCl extracts, our method is able to identify fine-scale spatial changes in bark pH that are relevant for the colonization of bark by organisms.German Research Foundation (DFG) [SFB 552.