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

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

Regional Sources and Seasonal Variability of Rainwater Dissolved Organic and Inorganic Nitrogen at a Mid-Atlantic, USA Coastal Site

Changes in anthropogenic activities have altered the speciation and concentration of inorganic reactive nitrogen (Nr) delivered to coastal and oceanic waters with precipitation. Less is known about rainwater dissolved organic nitrogen (DON) despite its quantitative importance (\u3e20% of Nr) and potential contributions to primary and secondary production. We document decreases in rainwater nitrogen and carbon amounts between 1994 and 2019 in Delaware, USA with the major reduction observed for nitrate (64%) reflecting emissions technology improvements. [DON] in 2019 was 55% that of 1994, though only 2 years of data are available precluding any assessment of trends. Season, airmass back trajectory (AMBT), rainfall amount, and meteorology influenced Nr amounts in 2018–2019 rain. [DON], which peaked in Summer, had different seasonal patterns than inorganic Nr and dissolved organic carbon, suggesting a biological source. Marine AMBT events showed the lowest Nr abundances. AMBTs from the southwest had the highest concentrations of Nr and DOC partially due to low rainfall amounts. Characterization of the oxidized fraction of DON revealed abundant highly unsaturated aliphatic and peptide-like formulas suggesting a combination of secondary organic, biomass burning, and biological sources. The large changes in Nr and DOC loads emphasize the dynamic nature of atmosphere to land/water fluxes due to the influence of anthropogenic processes with potential implications for coastal and oceanic water quality and ecology. Models of atmospheric deposition to watersheds and the ocean should be frequently reevaluated with current data to accurately assess inputs from changing atmospheric sources

Evaluation of an Instrumental Method to Reduce Error in Canopy Water Storage Estimates via Mechanical Displacement

To improve water budgeting of forested catchments and inform relevant hydrologic theory regarding forest water cycling, the scientific community has been seeking simple, inexpensive, direct methods for determining rainwater storage on in-situ tree canopies. This paper evaluates an installation arrangement/routine for one such method: mechanical displacement sensors placed on the trunk to directly monitor compression under canopy water loading from rainfall. The evaluated installation routine aligns mechanical displacement sensors along orthogonal axes passing through the trunk’s mechanical center to reduce wind-induced noise. Experimental attainment of neutral bending axes for a subject hard- and softwood tree suggest the routine is precise and approximates the trunk’s mechanical center well regardless of differences in cellular axial stiffness between heart and sapwood. When installed in this precise sensor arrangement, bending tests of different direction produced consistent signal ratios between sensor pairs about -1 (1 unit compression/1 unit elongation), allowing the identification and removal of bending strains from raw strain signals to isolate the compression component attributable to canopy water storage. The same experiments performed on sensors 5cm off the computed mechanical center were unable to produce neutral bending axes or consistent signal ratios during directional bending. Results from the method evaluation were translated into a data processing technique that is applied to strain data from 2 sample storms (1 each for the hardand softwood trees). Processed strain data showed clear synchronicities between rainfall and canopy loading, and periods of maximized canopy water loading (capacity). Our results indicate the evaluated arrangement/installation procedure for mechanical displacement sensors may provide scientists with simple, direct canopy water storage estimates at high temporal resolution and sensitivity

Instrumental Method to Reduce Error in Canopy Water Storage Estimates via Mechanical Displacement

To improve the water budgeting of forested catchments and inform relevant hydrologic theory regarding water cycling within forests, the scientific community has been seeking simple, inexpensive, direct methods for determining rain water storage on in situ tree canopies. We evaluate an installation arrangement and routine for one such method: mechanical displacement sensors placed on a tree’s trunk to directly monitor compression under canopy water loading from rainfall. The evaluated installation routine aligns mechanical displacement sensors along orthogonal axes passing through the mechanical center of the trunk to reduce wind-induced noise. The experimental attainment of neutral bending axes for a subject hard- and softwood tree suggest the routine is precise and approximates the trunk’s mechanical center well regardless of differences in cellular axial stiffness between heart and sapwood. When installed in this precise sensor arrangement, bending tests of different loading direction produced a consistent signal ratio between sensor pairs of approximately -1 (1 unit compression / 1 unit elongation), allowing the identification and removal of bending strains from the raw strain signals to isolate the compression component attributable to canopy water storage loads. The same experiments performed on sensors just 5 cm off the trunk’s computed mechanical center were unable to produce neutral bending axes or consistent signal ratios during bending from variable loading directions. Results from the method evaluation were translated into a data processing technique that is then applied to strain data collected through 2 sample rain events (1 each for the hard- and softwood trees). The processed strain data showed a clear synchronicity between rainfall and canopy loading, as well as periods of maximized canopy water loading (canopy storage capacity). Our results indicate that the evaluated arrangement and installation procedure for mechanical displacement sensors may be able to provide scientists with simple, direct canopy water storage estimates at high temporal resolution and sensitivity

Evaluation of an Instrumental Method to Reduce Error in Canopy Water Storage Estimates via Mechanical Displacement

To improve the water budgeting of forested catchments and inform relevant hydrologic theory regarding water cycling within forests, the scientific community has been seeking simple, inexpensive, direct methods for determining rain water storage on in situ tree canopies. This paper evaluates an installation arrangement and routine for one such method: mechanical displacement sensors placed on a tree\u27s trunk to directly monitor compression under canopy water loading from rainfall. The evaluated installation routine aligns mechanical displacement sensors along orthogonal axes passing through the mechanical center of the trunk to reduce wind-induced noise. The experimental attainment of neutral bending axes for a subject hardwood and softwood tree suggests the routine is precise and approximates the trunk\u27s mechanical center well regardless of differences in cellular axial stiffness between heart and sapwood. When installed in this precise sensor arrangement, bending tests of different loading directions produced a consistent signal ratio between sensor pairs of approximately −1 (1 unit compression/1 unit elongation), allowing the identification and removal of bending strains from the raw strain signals to isolate the compression component attributable to canopy water storage loads. The same experiments performed on sensors just 5 cm off the trunk\u27s computed mechanical center were unable to produce neutral bending axes or consistent signal ratios during bending from variable loading directions. Results from the method evaluation were translated into a data processing technique that is then applied to strain data collected through two sample rain events (one each for the hardwood and softwood trees). The processed strain data showed a clear synchronicity between rainfall and canopy loading, as well as periods of maximized canopy water loading (canopy storage capacity). Our results indicate that the evaluated arrangement and installation procedure for mechanical displacement sensors may be able to provide scientists with simple, direct canopy water storage estimates at high temporal resolution and sensitivity