► Land cover strongly influenced ecosystem water fluxes. ► Woody covers showed higher evapotranspiration rates than herbaceous covers. ► Native forests and eucalyptus plantations displayed similar ...evapotranspiration rates. ► Soil profiles were drier under woody plots. ► Liquid water fluxes were at least doubled in herbaceous covers.
Vegetation exerts a strong control on water balance and key hydrological variables like evapotranspiration, water yield or even the flooded area may result severely affected by vegetation changes. Particularly, transitions between tree- and herbaceous-dominated covers, which are taking place at increasing rates in South America, may have the greatest impact on the water balance. Based on Landsat imagery analysis, soil sampling and hydrological modeling, we evaluated vapor and liquid ecosystem water fluxes and soil moisture changes in temperate Argentina and provided a useful framework to assess potential hydrological impacts of vegetation cover changes. Two types of native vegetation (grasslands and forests) and three modified covers (eucalyptus plantations, single soybean crop and wheat/soybean rotation) were considered in the analysis. Despite contrasting structural differences, native forests and eucalyptus plantations displayed evapotranspiration values remarkably similar (∼1100mmy−1) and significantly higher than herbaceous vegetation covers (∼780, ∼670 and ∼800mmy−1 for grasslands, soybean and wheat/soybean (Triticum aestivum L., Glycine max L.) system, respectively. In agreement with evapotranspiration estimates, soil profiles to a depth of 3m were significantly drier in woody covers (0.31m3m−3) compared to native grasslands (0.39m3m−3), soybean (0.38m3m−3) and wheat/soybean rotation (0.35m3m−3). Liquid water fluxes (deep drainage+surface runoff) were at least doubled in herbaceous covers, as suggested by modeling (∼170mmy−1 and ∼357mmy−1, for woody and herbaceous covers, respectively). Our analysis revealed the hydrological outcomes of different vegetation changes trajectories and provided valuable tools that will help to anticipate likely impacts, minimize uncertainties and provide a solid base for sustainable land use planning.
An improved understanding of the drivers controlling infiltration patterns in semiarid regions is of key importance, as they have important implications for ecosystem productivity, retention of ...resources and the restoration of degraded areas. The infiltration depth variability (ΔInf) in vegetation patches at the hillslope scale can be driven by different factors along the hillslope. Here we investigate the effects of vegetation and terrain attributes under hypothesis that these attributes exert a major control in ΔInf within the patches. We characterise the ΔInf within vegetation patches at a semiarid hillslope located at the Jornada Experimental Range at dry antecedent conditions preceding two winter frontal rainfall events. We measured these events that are typical during winter conditions, and are characterised by low intensity (0.67 and 4.48 mm h−1) and a total rainfall of 10.4 and 4.6 mm. High precision geo-referenced wetting front depth measurements were taken at various locations within the vegetation patches using differential GPS. Vegetation and terrain attributes were analysed to explain the ΔInf among the vegetation patches. The infiltration depths in the periphery of the patches were in general considerably deeper than those in the centre. The observations suggest that the upslope margin of the patches received additional water in the form of runon from upslope adjacent bare soil. Patch orientation with regard to the slope dictated the effect of the rest of the patch attributes and the distance to the hillslope crest on ΔInf. We found that primarily patch orientation, followed by shape and size modulate lateral surface water transport through their effects on overland flow paths and water retention; something that would be obscured under more simplistic characterisations based on bare versus uniform vegetated soil discrimination.
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•Vegetation and terrain affect spatial variation in shallow infiltration depth.•Measurement of wetting front depths at various locations within vegetation patches•Infiltration depths are variable within the vegetation patches.•Infiltration variability is controlled by patch orientation, shape and terrain.•Patch orientation dictates patch shape and distance to hillslope crest effect.
► We discuss how ecosystem services can contribute to develop land-use policies. ► Tradeoffs between ecosystem services and disservices were analyzed. ► The link to nature was discussed in ...state-controlled and market-controlled policies.
Regular economic activity takes into account ecosystem goods and services that are exchanged for money in the market (e.g. food, fibre, water) but normally ignores more intangible ones left away from market transactions (e.g. soil protection, climate regulation, disturbance control, habitat provision), even in cases when they become irreversibly impaired. However, because of the increasing pressure brought by the public opinion, the attempts to assign an economic, yet volatile, valuation to ecosystems assets has multiplied in recent years, and policy communities are increasingly compelled to incorporate them into land use planning initiatives. Based on contributions to this special issue, we discuss how the perspective of ecosystem services can contribute to develop sound land-use policies and planning actions. Beyond valuation, several practical implications emerge from the contributions. A myriad of potential tradeoffs must be analyzed because since the provision of some services can be accompanied by the emergence of unexpected dis-services. For example, carbon accumulation based on increasing net primary production rates may simultaneously cut water yields and, hence, water provision. Various existing mechanisms ranging from state-controlled to market-controlled for rewarding the provision of ecosystem services are analyzed and discussed in terms of their capacity to connect nature to land-use planning.
Our knowledge about the functional foundations of ecosystem service (ES) provision is still limited and more research is needed to elucidate key functional mechanisms. Using a simplified ...eco-hydrological scheme, in this work we analyzed how land-use decisions modify the partition of some essential regulatory ES by altering basic relationships between biomass stocks and water flows. A comprehensive meta-analysis and review was conducted based on global, regional and local data from peer-reviewed publications. We analyzed five datasets comprising 1348 studies and 3948 records on precipitation (PPT), aboveground biomass (AGB), AGB change, evapotranspiration (ET), water yield (WY), WY change, runoff (R) and infiltration (I). The conceptual framework was focused on ES that are associated with the ecological functions (e.g., intermediate ES) of ET, WY, R and I. ES included soil protection, carbon sequestration, local climate regulation, water-flow regulation and water recharge. To address the problem of data normality, the analysis included both parametric and non-parametric regression analysis. Results demonstrate that PPT is a first-order biophysical factor that controls ES release at the broader scales. At decreasing scales, ES are partitioned as result of PPT interactions with other biophysical and anthropogenic factors. At intermediate scales, land-use change interacts with PPT modifying ES partition as it the case of afforestation in dry regions, where ET and climate regulation may be enhanced at the expense of R and water-flow regulation. At smaller scales, site-specific conditions such as topography interact with PPT and AGB displaying different ES partition formats. The probable implications of future land-use and climate change on some key ES production and partition are discussed.
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•The partition of regulatory services in ecosystems poses a major policy challenge.•We examined how partitions occur at the hydrosphere-anthroposphere intersection.•Five data sources were processed through meta-analysis.•Humans can exert some control ES partitioning through aboveground biomass changes.•Human control on ecosystem service partition increases at decreasing spatial scales.
Dry subtropical regions, originally hosting xerophytic vegetation, are currently characterized by diverse land cover/use patterns. Using existing biophysical and socio-economic databases, we explored ...how human contexts influenced land cover, vegetation composition and agricultural production in five distant regions. On average, cultivated areas represented a minor proportion (<16%) of all the regions, except in Asia (74%). This proportion was positively associated with population density when considering all regions together (slope = 0.2 ha∗inh
−1), but the association became weaker in low-population regions. While protected areas displayed highly similar life-forms across regions, non-protected natural vegetation areas presented large contrasts, suggesting different imprints of land management. The observed contrasts were more marked for cultivated vegetation, with different species and species diversities being found in each region. These contrasts likely reflect orientation toward national/global markets in the Australian and American regions and toward local markets/subsistence in Asian and African regions. Africa and Asia were characterized by low and similar per capita levels of food production (∼50 kg grain∗y
−1∗inh
−1 and ∼0.14 livestock units∗inh
−1), in contrast to South America and Australia (585 kg grain∗y
−1∗inh
−1 and 10.2 units∗inh
−1, respectively). This comparative perspective assisted in exploring the reciprocal influences between social-economic development and ecosystems that lead to alternative strategies of land management.
► Dry subtropical regions display contrasting land cover patterns across continents. ► Vegetation divergence increase from natural to seminatural to cultivated systems. ► Cultivated area increases with population density or connection to global markets. ► In spite of degradation contrasts, Asia and the Americas host similar grain yields. ► Per-capita grain outputs are low and convergent in Asia and Africa (50 kg∗y
−1∗inh
−1)
•Topography and land-use strongly affected salinization patterns.•Land-use had a stronger influence than topography on salinity patterns.•Tree plantations stored >7 times more salts in soils than ...croplands and grasslands.•Resistivity imaging allowed a cost-effective description of salinity patterns and mechanisms.
Being one of the oldest and most serious environmental problems, soil and groundwater salinization poses critical challenges for the managing of agricultural and natural areas. Together with climate, topography and land-use are main controls dictating salt accumulation patterns at different spatial scales. In this paper, we quantified the response of salt accumulation to the interactive effects of topography (lowland-upland gradients) and vegetation (annual crops, tree plantations, native grasslands) across a sub-humid sedimentary landscape with shallow groundwater in the Inland Pampas of Argentina. We measured salt stocks from the surface down to the water-table through soil coring and their horizontal distribution through electrical-resistivity imaging in eleven fields occupied by annual crops, eucalyptus plantations and grasslands, encompassing water-table depth gradients of 1–6m below the surface. Land-use and topography exerted strong influences on salinity and explained together 82% and 66% of the spatial variability of groundwater salinity and soil salt accumulation (0–2m of depth), respectively. As a single explanatory variable, land-use overwhelmed topography dictating salinity patterns. Tree plantations stored 7–8 times more salts than croplands and grasslands throughout the unsaturated soil profile in areas with shallow water-tables (<3.5-m depth). As groundwater became shallower, its salinity and that of the unsaturated soil above it increased, although the slope of this relationship was significantly higher in tree plantations. Soil salinity profiles and electrical-resistivity imaging showed maximum salinization around the water-table in tree plantations, indicating that groundwater absorption and solute exclusion by tree roots may be the dominant salinization mechanism. Our study highlights the strong influence of land-use on salinization patterns, which can be even stronger than the more widely recognized controls of climate and topography, and proposes some guidelines for a better use of vegetation to manage hydrology in salt-affected areas. A poor comprehension of this influence, as well as its underlying mechanisms, may lead to incorrect diagnosis of salinization and the implementation of ineffective management actions.
In arid regions throughout the world, shallow phreatic aquifers feed natural oases of much higher productivity than would be expected solely from local rainfall. In South America, the presence of ...well-developed
Prosopis flexuosa
woodlands in the Monte Desert region east of the Andes has puzzled scientists for decades. Today these woodlands provide crucial subsistence to local populations, including descendants of the indigenous Huarpes. We explore the vulnerability and importance of phreatic groundwater for the productivity of the region, comparing the contributions of local rainfall to that of remote mountain recharge that is increasingly being diverted for irrigated agriculture before it reaches the desert. We combined deep soil coring, plant measurements, direct water-table observations, and stable-isotopic analyses (
2
H and
18
O) of meteoric, surface, and ground waters at three study sites across the region, comparing woodland stands, bare dunes, and surrounding shrublands. The isotopic composition of phreatic groundwaters (δδ
2
H: −−137‰‰ ±± 5‰‰) closely matched the signature of water brought to the region by the Mendoza River (−−137‰‰ ±± 6‰‰), suggesting that mountain-river infiltration rather than in situ rainfall deep drainage (−−39‰‰ ±± 19‰‰) was the dominant mechanism of recharge. Similarly, chloride mass balances determined from deep soil profiles (>6 m) suggested very low recharge rates. Vegetation in woodland ecosystems, where significant groundwater discharge losses, likely >100 mm/yr occurred, relied on regionally derived groundwater located from 6.5 to 9.5 m underground. At these locations, daily water-table fluctuations of ∼∼10 mm, and stable-isotopic measurements of plant water, indicated groundwater uptake rates of 200-–300 mm/yr. Regional scaling suggests that groundwater evapotranspiration reaches 18-–42 mm/yr across the landscape, accounting for 7-–17%% of the Mendoza River flow regionally. Our study highlights the reliance of ecosystem productivity in natural oases on Andean snowmelt, which is increasingly being diverted to one of the largest irrigated regions of the continent. Understanding the ecohydrological coupling of mountain and desert ecosystems here and elsewhere should help managers balance production agriculture and conservation of unique woodland ecosystems and the rural communities that rely on them.
•Deeper water-table levels were observed in dairy compared to grain production systems.•Croplands showed higher soil moisture and enhanced groundwater recharge.•Pastures exhibited higher ...transpiration rates and direct groundwater discharge.•We found a strong association between the plot water balance and regional flooding.•Hydrological modeling suggested higher flooding risks in grain production systems.
Although the strong influence of vegetation shaping the hydrological cycle is increasingly recognized, the effects of land-use changes in very flat regions (i.e., hyperplains, regional slope <0.1%) are less understood in spite of their potentially large magnitude. In hyperplains with sub-humid climates, long-lasting flooding episodes associated to water-table raises are a distinctive ecohydrological feature and a critical environmental concern. We evaluated the hydrological impacts caused by the replacement of livestock systems, dominated by perennial alfalfa pastures, by grain production systems, dominated by annual crops, that have been taking place in the Pampas (Argentina). For this purpose, we combined remote sensing estimates of vegetation transpiration and surface water coverage with long-term (1970–2009) hydrological modeling (HYDRUS 1D), and water-table depth and soil moisture measurements. The NDVI derived from MODIS imagery was 15% higher in dairy systems than in grain production ones, suggesting higher transpiration capacity in the former (852 vs. 724mmy−1). Even higher contrasts were found among individual cover types, with perennial pastures having the highest NDVI and transpiration potential rates (0.66 and 1075mmy−1), followed by double winter/summer crops (0.55 and 778mmy−1) and single summer crop (0.45 and 679mmy−1). Significantly deeper long-term average water-table levels in dairy system compared to single and double cropping (4m, 1.5m and 2.1m, respectively) were suggested by the hydrological modeling and confirmed by field observations at nine paired sites (pasture vs. cropland, p<0.05) and two transects. At two additional paired sites, continuous water-table depth monitoring with pressure transducers, provided insights about the mechanisms behind these contrasts, which included enhanced groundwater recharge in the cropland and direct groundwater discharge by the pasture. Soil profiles, being notably drier under pastures (316 vs. 552mm stored at 0–3m depth, p<0.05), prevented the recharge episodes experienced by agricultural plots after an extraordinary rainy period. Our study highlights the key role of land-use on the hydrology of subhumid hyperplains, supporting the linkage of groundwater level raises and flood frequency and severity increases with the expansion of grain production systems in the Pampas. Given the spatial connectivity imposed by the hydrologic system and the strong association observed between the plot water balance and regional flooding, it is highly relevant to improve the quantification of the hydrological responsibility and interdependence of land use decision across plots and farms. This further step should support territorial policies that optimize the hydrological services of the region.
In regions with shallow water tables, ground water may have a positive (water supply) or negative (waterlogging or salinization) impact on crops. Reciprocally, crops can influence ground water, ...altering water table depth and chemical composition. We quantified these reciprocal influences along natural gradients of groundwater depth in flat sedimentary landscapes of the Inland Pampas occupied by wheat, soybean, and maize during two growing seasons (2006/2007 and 2007/2008). We correlated crop yield and groundwater depth maps at the field level and made direct plant, soil and groundwater observations at the stand level across topographic gradients. Water table level largely accounted for spatial crop yield variation, explaining 20–75% of their variance. An optimum groundwater depth range, where crop yields were highest, was observed for all three crop species analyzed (1.40–2.45
m for maize, 1.20–2.20
m for soybean, and 0.70–1.65
m for wheat). The areas within these optimum bands had yields that were 3.7, 3 and 1.8 times larger than those where the water table was below 4
m for wheat, maize, and soybean, respectively. As groundwater levels become shallower than these depth bands, crop yields declined sharply (∼0.05
kg
m
−2 on average for every 10
cm increase in water table level), suggesting negative effects of waterlogging, root anoxia and/or salinity. Groundwater levels below these depth bands were associated with gradually declining yields, likely driven by poorer groundwater supply.
Crops influenced groundwater levels through their control of recharge and discharge fluxes. The presence of active crops prevented recharge events (sharp water table level rises) observed during rainy periods in fall and spring. Crops consumed ground water generating increasing discharge as the water table depth decreased. This consumption led to rising soil and groundwater salinization towards shallower water table positions as the growing season progressed. The electrical conductivity of ground water for maize at maturity doubled the pre-sowing values (∼2.2
dS
m
−1 vs. ∼1.1
dS
m
−1,
p
<
0.01,) when ground water was above 2-m depth, whereas negligible changes were observed when groundwater depth exceeded 3.5
m. In flat humid landscapes, such as the Inland Pampas, crops and shallow ground water may be closely connected and influence each other through different mechanisms, posing both opportunities and risks for agricultural systems. Understanding these complex interactions could help raise and stabilize yields and provide keys to regulate the labile hydrology of these plains.
Although the bulk of plant biomass contains relatively light, atmospherically derived elements (C, H, O, N, and S), 5-10% of biomass is composed of heavier elements from soil minerals, such as Ca, ...Mg, K, and P. Plant uptake and cycling transport these heavier elements to the soil surface, resulting in shallower vertical distributions for strongly cycled elements than for other elements. In this paper, we evaluate the biogeochemical consequences of this process at different spatial and temporal scales based on chronosequence studies and soil database analyses. In the bare coastal dunes of Argentina, the vertical distributions of exchangeable K+(strongly cycled) and Na+(more weakly cycled) were similar initially but diverged 15 years after pine afforestation, with K distributions becoming significantly concentrated in the surface and Na distributions becoming deeper. To evaluate the effects of plant stoichiometry on micronutrient distributions, chronosequences of paired native grasslands (low Mn cycling) and eucalypt plantations (high Mn cycling) in the pampas of Argentina were also used. Within 50 years, eucalypts dramatically redistributed Mn pools toward the soil surface, reducing total pools by half at medium depths (20-60 cm) and increasing concentrations by up to an order of magnitude at the surface. Globally, we used generalized contrasts among exchangeable K, Na, and Mg in 7661 soil profiles to estimate the global magnitude of K uplift due to plant activity. Based on this calculation, the exchangeable K pool in the top 20 cm of soils without plant uplift would be 4-6 × 1015g smaller globally, one-third to one-half smaller than its current size. Vegetation change alters the vertical distribution and bioavailability of mineral elements. Understanding how the stoichiometry of plant cycling affects soil nutrient distributions will help refine predictions of the biogeochemical consequences of current vegetation change.
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