This special issue “Impact of climate change on physical and biogeochemical processes in the hydrologic cycle” presents a collection of articles on interactions of climatic drivers and hydro-biogeochemical responses as well as the role of biogeochemical processes in controls and feedbacks with regard to climate change impact. While the in-depth disciplinary studies are critically needed as presented in this issue, we also strongly believe that systems approach transcending disciplinary boundaries is needed to address the climate change in integrated natural and human systems.
Aims: Soil black carbon (BC) has been shown to possess large amounts of cation exchange sites and surface charge, and is viewed as a potential soil amendment to improve nutrient retention and for pollutant remediation. This study investigated the nano-scale distribution of reactive functional groups and the binding of cations on the surface of micron-size BC particles, identified the key processes, and explored the sources of surface functionality and their relative contribution to cation exchange capacity (CEC). Materials and Methods: Elemental microprobe and synchrotron-based Scanning Transmission X-ray Spectromicroscopy (STXM) coupled with Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy were used for nano-scale mapping of cations and reactive functional groups, and further distinction of the sources of reactive functional groups generated either by oxidation of BC surfaces or by adsorption of non-BC organic matter onto the BC surfaces. Their respective contribution to cation adsorption was obtained using a depth profile of a BC-rich Anthrosol from the central Amazon, Brazil. Results and Discussion: Adsorption of Non-BC organic matter is more dominant on the surface of BC particle in topsoil as evidenced by a stronger signal of microbial biomass and humic substances extracts. In comparison, a greater level of oxidation was found on the outerlayer of BC particles in subsoil horizons. Organic C in subsoils was found to generate 23-42% more CEC per unit C than topsoil. Based on CEC per unit C, the capacity of BC in creating CEC was 6-7 times higher than Non-BC, and the BC in deeper horizons had up to 20% higher CEC than the topsoil horizon. Near BC surfaces, higher ratios of Ca/C and K/C in subsoil than topsoil horizons reinforce the observation that BC in subsoil horizons had a higher capacity in binding cations and creating CEC than in the topsoil horizon. Conclusions: Oxidation of BC is suggested to be more efficient and important for creating CEC than the adsorption of non-BC onto BC surfaces, thus identified as being key for BC surface functionality and nutrient retention in Amazon Anthrosols.
Aims: To determine whether addition of inorganic nitrogen (N) directly to maize litter (stalk and leaf) with differing tissue quality impacts litter and soil organic matter (SOM) decomposition. We tested whether N addition leads to 1) faster litter decomposition, 2) less SOM-C decomposition and 3) increased incorporation of organic-C into soil-C fractions thereby increasing C sequestration potential in maize-based systems. Methodology: We investigated decomposition of two types of maize litter (stalk and leaf) with differing tissue quality both in the field and in a laboratory incubation experiment. In the field, litter was placed on the soil surface and at 10 cm soil depth to investigate the effect of litter burial and N addition on litter decomposition. Litter was harvested at six and twelve month intervals. In the incubation experiment, maize and stalk litter was ground and incorporated into the soil and incubated at 25ºC for 120 days. We measured CO2-C evolved and employed δ13C natural abundance differences between litter-C and SOM-C to measure both litter-C and SOM-C decomposition. At the end of the experiment, we examined soil-C storage via soil physical fractionation. Results: Exogenous N addition to litter had little effect both litter and SOM decomposition in the field and the laboratory except for in the stalk litter treatment where there was an 8% decrease in litter-C loss and a 5% increase in SOM-C loss in the laboratory incubation experiment. N addition to litter increased decomposition of litter in the first 20 days of litter decomposition in the laboratory incubation experiment, but reduced litter decomposition rates after day 20. N addition to litter had very little effect on C storage in soil aggregates. In the field, litter placement, and physical litter structure influenced decomposition much more than N inputs. Thus, adding N to litter is not an effective strategy to sequester C in maize-based systems.
Assessing the impacts of climate changes on water quality requires an understanding of the biogeochemical cycling of trace metals. Evidence from research on alluvial aquifers and coastal watersheds shows direct impacts of climate change on the fate and transformation of trace metals in natural environments. The case studies presented here use field data and numerical modeling techniques to test assumptions about the effects of climate change on natural arsenic contamination of groundwater in alluvial aquifers and mercury bioaccumulation in coastal salt marshes. The results show that the rises of sea level and river base during the warm Holocene period has led to an overall increase in groundwater arsenic concentration due to the development of reducing geochemical conditions and sluggish groundwater movement. Modeling results indicate that the intrusion of seawater occurring during high sea-level stand may lead to desorption of arsenic from surface of hydrous oxides due to pH effects and ionic competition for mineral sorbing sites. Our results also show that contamination and bioaccumulation of Hg and other metals in estuarine and coastal ecosystems may be influenced by climate-induced hydrologic modifications (atmospheric deposition, riverine input, salinity level, etc.).
This study investigates the potential change in the hydrologic cycle in Nzoia basin, one ofthe semi-arid basins of east Africa. An ensemble of 16 Global Climate Models data under different emissions scenarios are used in this study. The basin is expected to receive an increase in precipitation in all scenarios; from 5% to 15% by theend of this century compared to the base period 1990-1999. However, a 2 to 5ºC increase in temperature is expected to create an overall drier climate with reduced runoffs. The decadal averaged seasonal trends show that all major hydrological components except the runoff are expected to increase. An increase in temperature, together with more precipitation, could significantly increase actual evapotranspiration, ultimately may result a decrease in runoff by 14% and 18% in the 2020s and 2090s respectively compared to the base period. The elasticity analysis showed that the change in runoff is more sensitive to a change in temperature than precipitation for the 2060s and 2090s; and suggested that temperature will continue to be the dominating factor in future climate. In general, Nzoia will very likely experience a drier climate, further exacerbating the biomass production and food security.
Aims: In this paper, we aim to assess different parameterization schemes for quantifying the surface energy portioning process, in particular, the latent and sensible heat fluxes, and their applicability to various surface cover types. Study Design: This study intercompares theoretical models that predict the relative efficiency of the latent heat (evapotranspiration) with respect to the sensible heat flux. Model predictions are compared with field measurements over surface covers with different physical characteristics and soil water availability. Place and Duration of Study: This study was carried out at the Arizona State University, Tempe, AZ, between August 2012 and December 2012. Methodology: Three theoretical models for prediction of the relative efficiency of the latent heat were investigated, based on the lumped heat transfer (Priestley), the linear stability analysis (LSA) and the maximum entropy principle (MEP), respectively. Model predictions were compared against field measurements over three different land cover types, viz. water, grassland and suburban surfaces. An explicit moisture availability parameter β is incorporated in the MEP model, to facilitate direct comparison against the LSA and field measurements. Standard post-processing and quality control were applied to field measured turbulent fluxes using the eddy-covariance (EC) technique. To be consistent with the premise of all theoretical models, diurnal series of sensible and latent heat fluxes were filtered such that only data points under convective conditions were selected. Results: Among all three models, the application of Priestley model is restricted to saturated land surfaces, and generally overestimates the relative efficiency of the latent heat for water-limited surfaces. The LSA and MEP models predict similar β ranges, i.e., 0.05-0.3 in summer and 0.1-0.7 in winter over suburban area, and 0.1 to 0.5 over lake surface. Over vegetated surfaces, the MEP model predicts a reasonable β range around unity by taking transpiration into consideration, while the LSA model consistently underestimated the relative efficiency. Conclusion: Moisture availability plays an essential role in regulating the surface energy partitioning process. The introduction of the moisture availability parameter enables versatile theoretical models for latent heat (and evapotranspiration) predictions over a wide range of land cover types. This study provides a physical insight into the thermodynamics mechanism governing the surface energy balance, and the potential to develop novel surface energy parameterization schemes based on the concept of relative efficiency. The MEP model is found to have the greatest potential in terms of future theoretical model development.
Aims: This study is to evaluate the effect of petroleum crude oil contaminated soil on the mineral nutrient elements, soil properties and bacterial biomass of the rhizosphere of jojoba plants (Simmodsia chinensis). Methodology: A pot experiment was carried out. The soil was treated with different levels of crude oil: 1, 2 and 3% v/w either alone or in combination with inorganic fertilizers. Results: Malondialdehyde (MDA) concentration increased in jojoba leaves when grown in petroleum oil polluted soil especially at 2% and 3% crude oil. It was noted that, Na, Mg and Ca decreased while K increased in shoots of jojoba. In roots Na and Ca increased however K and Mg decreased with increasing crude oil concentration in the soil. Heavy metals, Cu, Mn, Cd and Pb increased in both shoot and root with increasing crude oil concentration while, Zn decreased comparing with the control. In soil, N and K decreased meanwhile Cu, Fe, Mn and Zn as well as organic matter increased with increasing crude oil concentration. Soil was free from P while, the addition of inorganic fertilizers improved P content. Bacterial account was significantly increased at the end of the experiment at 1% and 2% crude oil especially after addition of inorganic fertilizers. The electric conductivity and MDA of the leaves increased with increasing crude oil concentration. The addition of inorganic fertilizers to crude oil contaminated soil decreased the electric conductivity and MDA comparing with crude oil only. Conclusion: The observed changes in composition of mineral elements in jojoba plants in the present study could be attributed to the cell injury and disruption in the cell membrane, heavy metal accumulation and toxic nature of the petroleum oil. Also this study has demonstrated that soil contamination with crude oil has a highly significant effect of reducing some mineral element composition of Jojoba plants.