National Park Wetlands Research Articles

Interception and Redistribution of Precipitation by Parkinsonia aculeata L.: Implications for Palo Verde National Park Wetlands, Costa Rica

Seasonal wetlands in the tropics are important habitats for local and migratory bird species. In the northwestern Pacific of Costa Rica, Palo Verde National Park has one of the most important seasonal wetlands of Central America. The management history of this wetland has shown the impact of invasive plant species such as Parkinsonia aculeata L. whose cover extension and canopy structure impact not only the ecological niches of bird species, but also the wetland hydrology. A 300 m2 plot was established in a P. aculeata stand to evaluate the role of P. aculeata on the partitioning and redistribution of precipitation. Gross precipitation (PGr), throughfall (PTF) and stemflow (PSF) were measured on a daily basis to determine the interception of precipitation (PI) and net precipitation (PNet). A total of 43 precipitation events were sampled during the wet season of 2003. We measured 530.5 mm of PGr and 458 mm of PTF, with an average sampling error of 0.7 mm or 6.1%. Canopy storage capacity was estimated at 1.47 mm, throughfall 88.73%, stem flow 2.63% and a total interception of 8.64%, with a PNet coefficient of 0.9475. The relationships between gross precipitation (PGr) with throughfall (PTF), stemflow (PSF) and net precipitation (PNet) were evaluated using linear regression models. P. aculeata showed to have one of the highest net precipitation and lowest precipitation interception among small trees.

Hyperspectral reflectance measurements from UAS under intermittent clouds: Correcting irradiance measurements for sensor tilt

One great advantage of optical hyperspectral remote sensing from unmanned aerial systems (UAS) compared to satellite missions is the possibility to fly and collect data below clouds. The most typical scenario is flying below intermittent clouds and under turbulent conditions, which causes tilting of the platform. This study aims to advance hyperspectral imaging from UAS in most weather conditions by addressing two challenges: (i) the radiometric and spectral calibrations of miniaturized hyperspectral sensors; and (ii) tilting effects on measured downwelling irradiance. We developed a novel method to correct the downwelling irradiance data for tilting effects. It uses a hybrid approach of minimizing measured irradiance variations for constant irradiance periods and spectral unmixing, to calculate the spectral diffuse irradiance fraction for all irradiance measurements within a flight. It only requires the platform's attitude data and a standard incoming light sensor. We demonstrated the method at the Palo Verde National Park wetlands in Costa Rica, a highly biodiverse area. Our results showed that the downwelling irradiance correction method reduced systematic shifts caused by a change in flight direction of the UAS, by 87% and achieving a deviation of 2.78% relative to a on ground reference in terms of broadband irradiance. High frequency (< 3 s) irradiance variations caused by high-frequency tilting movements of the UAS were reduced by up to 71%. Our complete spectral and radiometric calibration and irradiance correction can significantly remove typical striped illumination artifacts in the surface reflectance-factor map product. The possibility of collecting precise hyperspectral reflectance-factor data from UAS under varying cloud cover makes it more operational for environmental monitoring or precision agriculture applications, being an important step in advancing hyperspectral imaging from UAS.

Coupling high-resolution field monitoring and MODIS for reconstructing wetland historical hydroperiod at a high temporal frequency

Historical wetland hydrology data are instrumental to support the design of wetland management and restoration strategies but are rarely available. In this study, we tested the capabilities and limitations of a simple methodological framework based on publicly available MODIS Land Reflectance Products to estimate wetland soil surface saturation and inundation spatiotemporal dynamics. Using supervised learning and high-resolution groundwater and surface water elevation data, the framework searches for spectral algorithms, referred to as the wet/dry wetland status classifier (WSC) and the continuous wetland dynamics identifier (WDI), that best predict upper soil layer wetness status in the study wetland. We used Google Earth Engine (GEE) for fast access and processing of the full range of MODIS data. The capabilities of GEE also enabled us to readily conduct a comparative assessment of the MODIS 8-day composite and daily collections and test various pixel-level quality filters to select reliable data at the highest possible temporal resolution. We tested the framework on the internationally-recognized Ramsar site Palo Verde National Park wetland in Costa Rica, and we obtained good results (overall prediction accuracy of 86.6% and kappa coefficient of 0.7 for the WSC; r2 of 0.71 for the WDI). High-resolution water level data allowed us to assess the challenges, promises and limitations of using MODIS products for wetland hydrology applications. We then applied the WSC and WDI to map the 2000-2016 sub-weekly wetland hydroperiod at 500m resolution, achieving a temporal resolution rarely matched in remote sensing for wetland studies. The analysis of the end-products, combined with the field water elevation data, provided new insights into the drivers controlling the spatiotemporal dynamics of hydroperiod within the Palo Verde wetland and did not reveal any significant temporal trends. The WSC and WDI framework developed here can be useful for reconstructing long-term hydroperiod variability and uncovering its drivers for other wetland systems globally.

Reconciling Landscape Fragmentation and Hippopotamuses Population Decrease in Virunga National Park Wetland

Wetlands have been noted to be beneficial worldwide. Despite wetlands being a natural asset that is of great significance to the human community, they are threatened by human and natural events. In Virunga National Park (VNP) wetlands are the habitat of Hippopotamus (Hippopotamus amphibius) which are among the animal species threatened by extinction in VNP since the past few decades. As shown by the last studies the number of Hippos population declined for 96% for the period of less than 40 years. This study evaluated landscape fragmentation status and its implication on the decline of the hippos population in VNP wetland for the period from 1990 to 2018. This study’s land cover data was obtained using remote sensing techniques with the help of software package ERDAS IMAGINE v16.6 and ArcGIS v10.3. It was mapped and classified using the maximum likelihood supervised classification technique. The landscape was classified into seven classes, which included Cropland, Forest, grassland, wetland, scrubland, bare area, and water. Satellite data (Landsat) was used to evaluate NDVI and NDWI and finally the landscape patterns in the study were analyzed using Fragstats 4.2, which was also used to calculate landscape indices for the respective periods. The results obtained from the LULC, NDVI, NDWI and the landscape metrics showed that during the period of our study the VNP wetland was fragmented. A strong negative correlation between the number of hippos and the wetland’s LFI (Landscape Fragmentation Index) values showed that wetland fragmentation was one of the reasons of the decline of Hippos in the park.

Lessons learnt from semi-arid wetland degradation. Las Tablas de Daimiel National Park

The Tablas de Daimiel National Park wetland developed in an area characterized by the cyclic nature of droughts, excessive aquifer exploitation and an evident aridification trend driven by climate change. The park and its surroundings have been exploited since prehistoric times and they are currently deeply anthropized to the point that both the physical survival of the wetland as well as its ecological function entirely depend on human action. A severe drought between 2006 and 2009 together with the drawdown of the water table caused the dry out of the system, reed overgrowth, disappearance of cut-sedge and sub-aquatic Chara spp. meadows and a smouldering peat fire. During this same period surface water, soil and groundwater were sampled for physical, hydrological and hydrochemical characterization. Upon drainage, the system functions as an artificial recharge system and becomes eutrophic showing large nutrient and salt content in soils and water. High water transmissivity capacities in the unsaturated zone and anthropic park management (soil compacted by heavy machinery, recirculation of low quality groundwater, reed reaping, water transfers, etc.) condition groundwater pollution. Increased knowledge of the physical-environment has allowed us to build a conceptual model of the surface water – groundwater interactions and to develop management tools to support the park management during a system dry out. Amongst these actions, we propose an unsaturated flow model for soil moisture simulation than can be used to predict critical soil water content for reed overgrowth or peat combustion risk.

A Critical Evaluation on the Role of Aerodynamic and Canopy–Surface Conductance Parameterization in SEB and SVAT Models for Simulating Evapotranspiration: A Case Study in the Upper Biebrza National Park Wetland in Poland

Evapotranspiration (ET) estimation through the surface energy balance (SEB) and soil-vegetation-atmosphere-transfer (SVAT) models are uncertain due to the empirical parameterizations of the aerodynamic and canopy-substrate conductances (gA and gS) for heat and water vapor transfers. This study critically assessed the impact of conductance parameterizations on ET simulation using three structurally different SEB and SVAT models for an ecologically important North-Eastern European wetland, Upper Biebrza National Park (UBNP) in two consecutive years 2015 and 2016. A pronounced ET underestimation (mean bias −0.48 to −0.68 mm day−1) in SEBS (Surface Energy Balance System) was associated with an overestimation of gA due to uncertain parameterization of momentum roughness length and bare soil’s excess resistance to heat transfer (kB−1) under low vegetation cover. The systematic ET overestimation (0.65–0.80 mm day−1) in SCOPE (Soil Canopy Observation, Photochemistry and Energy fluxes) was attributed to the overestimation of both the conductances. Conductance parameterizations in SEBS and SCOPE appeared to be very sensitive to the general ecohydrological conditions, with a tendency of overestimating gA (gS) under humid (arid) conditions. Low ET bias in the analytical STIC (Surface Temperature Initiated Closure) model as compared to SEBS/SCOPE indicated the critical need for calibration-free conductance parameterizations for improved ET estimation.

Breeding in a Dry Wetland. Demographic Response to Drought in the Common Reed-Warbler Acrocephalus scirpaceus

Mediterranean wetlands show remarkable seasonal and annual variations in their hydroperiod, i.e. the period during which they are inundated. Climate change-induced hydroperiod reductions have been shown to affect marshland birds but more studies are needed to understand this process in Mediterranean wetlands. The present study shows the demographic response of the Common Reed-warbler Acrocephalus scirpaceus to an unusual and prolonged drought in the Tablas de Daimiel National Park wetland (central Spain). We used data from two constant effort mistnetting stations (2005–2013), and spatially explicit capture-recapture Jolly-Seber models. The Reed-warblers continued reproducing in a dry environment for three years after the start of a dry phase, despite progressive declines in productivity, and ultimately stopped nesting in the fourth year. After the recovery of water levels in subsequent years, the population required another four years to recover a size and productivity similar to those preceding the drought. This situation may be common in the near future given ongoing alterations of the hydroperiod in Mediterranean wetlands as a consequence of climate change and groundwater overexploitation. We also show that spatially explicit capturerecapture models allow the detection of changes in the populations of small passerines, and are an accurate approach to estimating their densities. —Jimenez, J., Hernandez, J.M., Feliu, J., Carrasco, M. & Moreno-Opo, R. (2018). Breeding in a dry wetland. Demographic response to drought in the Common Reed-warbler Acrocephalus scirpaceus. Ardeola, 65: 247–259.

Envisat/ASAR Images for the Calibration of Wind Drag Action in the Doñana Wetlands 2D Hydrodynamic Model

Doñana National Park wetlands are located in southwest Spain, on the right bank of the Guadalquivir River, near the Atlantic Ocean coast. The wetlands dry out completely every summer and progressively flood again throughout the fall and winter seasons. Given the flatness of Doñana’s topography, the wind drag action can induce the flooding or emergence of extensive areas, detectable in remote sensing images. Envisat/ASAR scenes acquired before and during strong and persistent wind episodes enabled the spatial delineation of the wind-induced water displacement. A two-dimensional hydrodynamic model of Doñana wetlands was built in 2006 with the aim to predict the effect of proposed hydrologic restoration actions within Doñana’s basin. In this work, on-site wind records and concurrent ASAR scenes are used for the calibration of the wind-drag modeling by assessing different formulations. Results show a good adjustment between the modeled and observed wind drag effect. Displacements of up to 2 km in the wind direction are satisfactorily reproduced by the hydrodynamic model, while including an atmospheric stability parameter led to no significant improvement of the results. Such evidence will contribute to a more accurate simulation of hypothetic or design scenarios, when no information is available for the atmospheric stability assessment.

Trade-offs in plankton species richness arising from drought: insights from long-term data of a National Park wetland (central Spain)

Wetlands are considered vulnerable ecosystems of both high species richness and socio-economic value. In semi-arid regions, these ecosystems often experience long drought periods that are usually aggravated by local water overexploitation. Drought leads to: (i) reduced flooding area, (ii) isolation of water bodies, (iii) increased areas of dry sediments and shoreline length, and (iv) increased ionic concentration. These processes affect aquatic populations in a species-specific way and can have antagonistic effects on taxon richness. Here, we highlight long-term (1997–2008) trade-off effects on plankton species richness linked to drought in a semi-arid wetland (Las Tablas de Daimiel National Park, central Spain). Annual average phytoplankton species richness increased from wet- (1997–1998) to dry years (2001–2002) and taxon richness diminished again when drought was more severe (2007–2008). Zooplankton changes were more complex depending on taxonomic groups and the body size of the organisms, total species loss being related to hydrological conditions. Half of the algal species recorded in 2007–2008 and one-tenth of total zooplankton taxa were new comers in the wetland, because salinization, eutrophication and submerged macrophytes occurring in different sites enhanced species turnover and mitigated homogenization of beta diversity. Maintenance of one water body with a constant water level and macrophytes was the key to preventing the collapse of plankton richness. Our study has demonstrated that plankton can be very useful for tracking environmental changes of wetlands, thus giving the environmental manager another tool to enhance the conservation of wetlands and their biota.

ASAR polarimetric, multi-incidence angle and multitemporal characterization of Doñana wetlands for flood extent monitoring

Doñana National Park wetlands, in South West Spain, undergo yearly cycles of inundation and drying out. During the hydrological year 2006–2007, 43 ASAR/Envisat images of Doñana, mostly in HH and VV polarizations, were acquired with the aim to monitor the flood extent evolution during an entire flooding cycle. The images were ordered in the seven ASAR incidence angles, also referred to as swaths, to achieve high observation frequency. In this study, backscattering temporal signatures of the main land cover types in Doñana were obtained for the different incidence angles and polarizations. Plots showing the σ 0HH/ σ 0VV ratio behavior were also produced. The signatures were analyzed with the aid of miscellaneous site data in order to identify the effect of the flooding on the backscattering. Conclusions on the feasibility to discriminate emerged versus flooded land are derived for the different incidence angles, land cover types and phenological stages: intermediate incidence angles (ASAR IS3 and IS4) came up as the most appropriate single swaths to discriminate open water surface from smooth bare soil in the marshland deepest areas. Flood mapping in pasture lands, the most elevated regions, is feasible at steep to mid incidence angles (ASAR IS1 to IS4). In the medium elevation zones, colonized by large helophytes, shallow incidence angles (ASAR IS6 and IS7) enable more accurate flood delineation during the vegetation growing phase. Since Doñana land covers require different observation swaths for flood detection, the composition of different incidence angle images close in time provides the optimum flood mapping. Such composition is possible four times per ASAR 35-day orbit cycle, using pairs of 12-h apart IS1/IS6 and IS2/IS5 Doñana images.

The role of multiple stressors in ranavirus-caused amphibian mortalities in Acadia National Park wetlands

Recent studies suggest that multiple sublethal stressors compromise amphibian immune systems and increase susceptibility to disease. We examined two aspects of multiple stressors and incidence of ranavirus-caused amphibian mortalities in free-living amphibian populations: (1) among-pond differences in physical, chemical, and biological stressors that may exacerbate mortality events, and (2) temporal changes in within-pond stressors that coincide with mortality events. At the among-pond scale, we used principal components analysis and logistic regression followed by Akaike’s information criterion (QAICc) to identify stressors associated with disease incidence. Of the stressors we investigated, aluminum, temperature, and conductivity were most correlated with outbreaks, but it was unclear whether they increased ranavirus-caused mortality events. Sublethal stressors were difficult to isolate in the field and few were significantly associated with ranavirus across all breeding ponds. Our results suggest that each wetland, because of varied physical, biological, and chemical settings, will have its own suite of stressors that sublethally affect amphibians.

Sustained primary production with changing phytoplankton assemblages in a semiarid wetland

This study has two main objectives, the first being the determination of net phytoplankton primary production to explain the phytoplankton’s function in a wetland carbon cycle, while the second objective is to relate this function with the phytoplankton assemblage composition. The annual variation in the phytoplankton production was monitored monthly for more than a year (2007–2008) in the semiarid eutrophic, hydrologically-perturbed “Tablas de Daimiel” National Park wetland. The phytoplankton fraction considered in this study comprised all organisms between the size 3 and 100 μm. The total biomass of phytoplankton was obtained by counting algae and calculating their volume, while net primary production and respiration were quantified by in situ incubations with the Winkler method. The respiration ranged from undetectable to 0.07 mgO2 l−1 h−1; net photosynthesis reached 0.20 mgO2 l−1 h−1. Net primary production was maximum at the end of the warm period (October 2007), and other peaks occurred at the start of summer (July 2007) or spring (March 2008). When maximum production took place, phytoplankton was mainly composed of small fast-growing chlorophytes (Tetraselmis cf. fontiana or Chlamydomonas sp.), in addition to some of the large, S-strategist algae (Peridinium umbonatum, Microcystis flos-aquae, Euglena sp.). The phytoplankton metabolism in “Tablas de Daimiel” was autotrophic as a whole due to changing contributions of algal groups. Only chlorophyte biomass was statistically related to net primary production. The conclusion reached is that this shallow eutrophic semiarid wetland possessed an annual net autotrophic production of phytoplankton fraction resulting from the small, fast-growing algae enhanced by hydrological perturbations that interrupted the autogenic course of S strategists.