Nitrogen/phosphorus behavior traits and implications during storm events in a semi-arid mountainous watershed

Seasonal rainfall events reinforce the link between terrestrial and fluvial domains and are crucial for assessing hydrological control over riverine nutrient dynamics and pollutant source behaviors, especially in a semi-arid watershed. Taking the Qingshuihe river basin, a semi-arid mountainous basin in China, as an example, this paper investigated storm effects on riverine nitrogen (N) and phosphorus (P) dynamics (i.e. concentration, load, and composition changes) through continuous sampling of four storm events of the 2019 rainy season, including one small storm, two moderate storms, and a large storm. Pollutant sources and transport pathways were then examined over the storm sequence via hysteresis analysis. The results revealed a strong linkage between N/P dynamics and hydrological processes. Storm runoff caused a 6-fold increase in particulate-P (PP) and a 4-fold increase in ammonia-N (NH₄-N) fluxes through four storms (most sensitive nutrients to storms). On average, PP shared 86% of P exports, and nitrate-N (NO₃-N) contributed 79% of N exports. PP and NH₄-N were delivered primarily from overland sources and transported by surface runoff. Nonetheless, mobilization of channel sediment reserves was also an important way of PP supply during storms. The results suggested groundwater as the principal NO₃-N source in the watershed, and subsurface flow was important for NO₃-N and total dissolved-P (TDP) delivery during storms. The large storm (>20 mm) often registered the highest N/P load exports. However, there were other influencing factors/processes on stormflow N/P dynamics in the semi-arid watershed, which complicate/override the effects of different storm magnitudes. Total suspended solids (TSS)/PP source availability and inter- and intra-storm export trends influenced P behaviors through storms. Moreover, impacts of mobilization processes on NO₃-N behavior appeared over the storm sequence. These findings enhance our understanding of storm events induced N/P exports in water-scarce regions and provide references for water quality predictions and control in flood seasons.

Homegardens as a multi-functional land-use strategy in Sri Lanka with focus on carbon sequestration

This paper explores the concept of homegardens and their potential functions as strategic elements in land-use planning, and adaptation and mitigation to climate change in Sri Lanka. The ancient and locally adapted agroforestry system of homegardens is presently estimated to occupy nearly 15 % of the land area in Sri Lanka and is described in the scientific literature to offer several ecosystem services to its users; such as climate regulation, protection against natural hazards, enhanced land productivity and biological diversity, increased crop diversity and food security for rural poor and hence reduced vulnerability to climate change. Our results, based on a limited sample size, indicate that the homegardens also store significant amount of carbon, with above ground biomass carbon stocks in dry zone homegardens (n = 8) ranging from 10 to 55 megagrams of carbon per hectare (Mg C ha(-1)) with a mean value of 35 Mg C ha(-1), whereas carbon stocks in wet zone homegardens (n = 4) range from 48 to 145 Mg C ha(-1) with a mean value of 87 Mg C ha(-1). This implies that homegardens may contain a significant fraction of the total above ground biomass carbon stock in the terrestrial system in Sri Lanka, and from our estimates its share has increased from almost one-sixth in 1992 to nearly one-fifth in 2010. In the light of current discussions on reducing emissions from deforestation and forest degradation (REDD+), the concept of homegardens in Sri Lanka provides interesting aspects to the debate and future research in terms of forest definitions, setting reference levels, and general sustainability.

REDD+ readiness implications for Sri Lanka in terms of reducing deforestation

Any system to compensate countries for reduced emissions from deforestation and forest degradation (REDD+) requires a historical reference level against which future performance can be measured. Here we examine the possibilities Sri Lanka, a small forest country with limited data on forest carbon stocks, has to get ready for REDD+. We construct a historical reference level using available forest inventory data combined with updated 2008 and 2009 in situ carbon density data for Sri Lankan forests. Furthermore, we use a combination of qualitative and quantitative data to attribute the clearing of Sri Lankan forests in the latest years for which national forest inventory data are available, 1992-1996, to various proximate drivers and to estimate the opportunity cost of forest conservation. We estimate that baseline deforestation emissions in Sri Lanka amounted to 17MtCO(2)yr(-1) in the 1992-1996 period, but conclude that it is challenging for Sri Lanka to produce a robust and accurate reference level due to the lack of nationally based inventories. We find that the majority of forest clearing (87%) is due to small-scale, rainfed farming, with the two other major drivers being rice and tea cultivation. Further, Sri Lankan revenues from REDD+ participation could be substantial, but they are sensitive to REDD+ policy transaction cost, highly uncertain timber revenues, and particularly the carbon price paid for emission reductions. The latter needs to be higher than $5-10/tCO(2) if there are to be substantial incentives for Sri Lanka to participate in REDD+. There is, however, a large gap in the knowledge of deforestation drivers that needs to be filled if Sri Lanka is to formulate an effective policy response to forest degradation in REDD+. For successful REDD+ implementation in Sri Lanka to happen, technological assistance, readiness assistance, and continued political momentum are crucial.

Growth and elemental accumulation by canola on soil amended with coal fly ash

To explore the agronomic potential of an Australian coal fly ash, we conducted two glasshouse experiments in which we measured chlorophyll fluorescence, CO2 assimilation (A), transpiration, stomatal conductance, biomass accumulation, seed yield, and elemental uptake for canola (Brassica napus) grown on soil amended with an alkaline fly ash. In Experiment 1, application of up to 25 Mg/ha of fly ash increased A and plant weight early in the season before flowering and seed yield by up to 21%. However, at larger rates of ash application A, plant growth, chlorophyll concentration, and yield were all reduced. Increases in early vigor and seed yield were associated with enhanced uptake of phosphorus (P) by the plants treated with fly ash. Fly ash application did not influence accumulation of B, Cu, Mo, or Zn in the stems at any stage of plant growth or in the seed at harvest, except Mo concentration, which was elevated in the seed. Accumulation of these elements was mostly in the leaves, where concentrations of Cu and Mo increased with any amount of ash applied while that of B occurred only with ash applied at 625 Mg/ha. In Experiment 2, fly ash applied at 500 Mg/ha and mixed into the whole 30 cm soil core was detrimental to growth and yield of canola, compared with restricting mixing to 5 or 15 cm depth. In contrast, application of ash at 250 Mg/ha with increasing depth of mixing increased A and seed yield. We concluded that fly ash applied at not more than 25 Mg/ha and mixed into the top 10 to 15 cm of soil is sufficient to obtain yield benefits.