Pampean Plain Research Articles

Evaluation of the hydrogeological response to neotectonics of the Quequén Grande River Watershed using geoelectrical methods

The Quequén Grande River Watershed (Southeast of Buenos Aires Province, Argentina) is a strong asymmetrical watershed in the Pampean Plain. It is marked by the stream capture of the Quequén Grande River eastward. The topographic slopes and hydraulic gradients are typically low in this area, with streams and rivers primarily effluent along their courses. This behavior is attributable to the influence of the unconfined and shallow Pampean aquifer, which serves as the region's main source of water supply. In the southwestern limit of this drainage basin, several shallow lakes, disconnected from the surface drainage network and related to an old deflation/accumulation relief, occur over hillock formations. In this area, Paleozoic rocks crop out and constitute the hydrological basement of the aquifer. The bedrock architecture of this formation could explain the stream piracy of the Quequén Grande River eastward and the local geomorphology, where structural lineaments related to neotectonic movements have been reported. However, there is a lack of information related to the hydrological basement in depth, which is needed to understand the surface water dynamics of this drainage basin, linked to the topographic control of the landscape. To fill this gap, a geoelectric model of the hydrological basement is proposed from 37 Vertical Electrical Soundings and 6 Electric Resistivity Tomographies, aiming to contribute to understanding this portion of the Earth's crust. Geoelectrical surveys were performed over 3000 km2 of the southwestern limit of the Quequén Grande River Watershed. Results obtained and field observations suggest the deviation of the Quequén Grande River catchment eastward is caused by the hydrogeological basement structure in depth, in response to neotectonic movements inferred by structural lineaments.

Environmental changes in the southeastern Pampa plain (southeastern South America) during the last millennium based on multiple lacustrine indicators and historical records

Environmental changes in the southeastern Pampa plain (southeastern South America) during the last millennium based on multiple lacustrine indicators and historical records

The missing sedimentological section linking the Neogene and quaternary of the Tandilia system and the Salado basin, Buenos Aires province, Argentina

The Tandilia system and the Salado basin are two adjacent morphostructural units located within the Argentine Pampean plain, each exhibiting distinct and independent geological histories. The Tandilia system preserves outcrops of Argentina's oldest Proterozoic rocks, while the sedimentary record of the Salado basin began during the Jurassic period. However, starting in the Cenozoic era, both units began to display common continental sedimentary fill characteristics. Despite this connection between the Tandilia system and the Salado basin, there is no unified lithostratigraphic framework for the Cenozoic that varies according to the studied localities. This study aims to define the stratigraphy of a sedimentary section that demonstrates the link between these morphostructural units from the Neogene onwards and to correlate it with the formal lithostratigraphic frameworks proposed in the literature. The analysis of well records led to the description of lithofacies and the establishment of facies associations, which were integrated to generate three correlation transects between the wells. Four facies associations were identified, three of which were fluvial and one aeolian. The analysis of these facies associations revealed that the sedimentary fill could be divided into two sedimentary sequences, lower sedimentary sequence and upper sedimentary sequence, separated by a sequence boundary marked by conglomeratic deposits. The definition of a stratigraphic framework for the middle section of the Del Azul creek basin and its correlation with the formal lithostratigraphic frameworks of the region indicate that from the Neogene onwards, both morphostructural units, the Tandilia system and the Salado basin, share sedimentological and tectonic characteristics. This study highlights the significance of subsurface information in understanding the geology of plain areas and its influence on regional geological evolution.

Analysis of subsurface data to characterize neotectonic structures in the Pampas plains, southwestern sector of the San Guillermo Elevated Block, Argentina

Analysis of subsurface data to characterize neotectonic structures in the Pampas plains, southwestern sector of the San Guillermo Elevated Block, Argentina

Factors and processes controlling hydrochemistry and evaporitic deposits in hypersaline wetland‐shallow lake systems

AbstractThree wetland‐shallow lakes were studied with the aim of analysing the processes and factors that control hydrochemistry and evaporite deposits in them in basins of the Pampean Plain, Argentina. In this sense, water balances and analysis of the water content of the lakes with normalized water difference index were made, and geologic‐geomorphological characteristics and groundwater flows were defined. Groundwater, surface water and evaporite samples were taken, along with sediment samples from wetland‐shallow lakes and surroundings. In situ pH, electrical conductivity and temperature, and laboratory chemical determinations of major ions of the water were measured. x‐ray diffraction (XRD) and scanning electron microscope (SEM)‐energy dispersive spectroscopy (EDS) analyses of evaporite and sediment samples were carried out. The results obtained allow the identification of two different systems. One of them is represented by Leubucó wetland‐lake basin, which is topographically higher and smaller than the other system, with Na‐HCO3 and Na‐Cl/SO4 groundwater inflows, with high concentrations of Ca2+ and Mg2+. In periods of high evaporation, the regional water table drops, and due to its topographic position, the lake dries. These determine the formation of thick layers of halite associated with magnesium salts on surface, and gypsum layers interbedded with clastic sediments. The other system involves de la Sal and Chasilauquen wetland‐lake basins, which have larger extensions. They receive Na‐HCO3 and Na‐Cl/SO4 groundwater inflow, but with low Mg2+ and Ca2+. Their lower topographic position determines that even during deficit periods, the water table intercepts the lakes surface and therefore, lakes have a shallow surface water level almost all the year, which is hypersaline, Na‐Cl type. These systems only have thin evaporite crusts, composed of halite and thenardite at the edges of the lakes, and the formation of Ca‐Mg sulfates is not observed. It is concluded that topographic position, basins size, geology, groundwater inflow and evaporation are the main processes and factors controlling hydrochemistry and evaporitic deposits.

Prediction of Evapotranspiration in the Pampean Plain from CERES Satellite Products and Machine Learning Techniques

A key aspect in agricultural zones, such as the Pampean Plain of Argentina, is to accurately estimate evapotranspiration rates to optimize crops and irrigation requirements and the floods and droughts prediction. In this sense, we evaluate six machine learning approaches to estimate the reference and actual evapotranspiration (ET0 and ETa) through CERES satellite products data. The results obtained applying machine learning techniques were compared with values obtained from ground-based information. After training and validating the algorithms, we observed that Support Vector machine-based Regressor (SVR) showed the best accuracy. Then, with an independent dataset, the calibrated SVR were tested. For predicting the reference evapotranspiration, we observed statistical errors of MAE = 0.437 mm d−1, and RMSE = 0.616 mm d−1, with a determination coefficient, R2, of 0.893. Regarding actual evapotranspiration modelling, we observed statistical errors of MAE = 0.422 mm d−1, and RMSE =0.599 mm d−1, with a R2 of 0.614. Comparing the results obtained with the machine learning models developed another studies in the same field, we understand that the results are promising and represent a baseline for future studies. Combining CERES data with information from other sources may generate more specific evapotranspiration products, considering the different land covers.

Prediction of Evapotranspiration in the Pampean Plain from CERES Satellite Products and Machine Learning Techniques

A key aspect in agricultural zones, such as the Pampean Plain of Argentina, is to accurately estimate evapotranspiration rates to optimize crops and irrigation requirements and the floods and droughts prediction. In this sense, we evaluate six machine learning approaches to estimate the reference and actual evapotranspiration (ET0 and ETa) through CERES satellite products data. The results obtained applying machine learning techniques were compared with values obtained from ground-based information. After training and validating the algorithms, we observed that Support Vector machine-based Regressor (SVR) showed the best accuracy. Then, with an independent dataset, the calibrated SVR were tested. For predicting the reference evapotranspiration, we observed statistical errors of MAE = 0.437 mm d−1, and RMSE = 0.616 mm d−1, with a determination coefficient, R2, of 0.893. Regarding actual evapotranspiration modelling, we observed statistical errors of MAE = 0.422 mm d−1, and RMSE =0.599 mm d−1, with a R2 of 0.614. Comparing the results obtained with the machine learning models developed another studies in the same field, we understand that the results are promising and represent a baseline for future studies. Combining CERES data with information from other sources may generate more specific evapotranspiration products, considering the different land covers.

Environmental assessment of water management and urban growth: A case study in an Argentina Pampean plain's basin

Urbanization has been identified as one of the issues with the greatest environmental impacts on water resources. This study aims to make an environmental diagnosis of urban water management with a systematic approach in a basin with great hydrogeological complexity. We have analyzed urban water management in the Langueyú basin, Argentina, in the period comprehended between 1940 and 2015 in which the city has had a disordered urban growth. It showed that the lack of integrated management together with urban expansion have resulted in a process of building densification and infrastructure that favors the recurrence and magnitude of exceptional hydrological events. This has been accompanied by a spatial displacement of these events and a lack of sanitary services with the same sense of urbanization. It was also demonstrated that the lack of integrated water management this not only had consequences on the Tandil city services associated with the urban hydrological cycle, but also on the quality of its surface water resources (contamination of streams in its urban section) and groundwater (elevation of nitrates levels in water from wells water supply). The absence of a systemic approach to the problem has not considered the relationships between the subsystems involved in water management. This management has been based mainly on the application of structural measures. The main non-structural measure carried out has been to expand the regulations and some neighbor's struggle movements. Other non-structural measures promoted by several actors involved in urban water management, such as authorities, should be carried out in order to raise awareness amongst the population on the importance of water resource protection, especially in areas with hydrogeological limitations.

A multi-tracer approach to quantifying groundwater discharge in flat areas

Identifying of groundwater discharge in surface waters is of outstanding interest in order to complete water balance models, understand the dynamics of surface hydrology, or quantify solute contribution, including nutrients and pollutants. This study aims to evaluate groundwater discharge into two small streams in the Atlantic coastal area of the Argentine Pampa Plain and ascertaining the relationship between groundwater age and 222Rn as a discharge indicator. In August 2017, samples were collected from two streams, La Ballenera and Vivoratá, and 222Rn activities, CFCs concentration, ionic composition, EC, and stable isotopes (δ18O, δ2H) were measured. The chemical composition and EC of the two streams was similar. The isotopic composition showed some difference in the Vivoratá stream among the samples close to the headwaters, which are more depleted and have a deuterium excess value similar to the ordinate of the local meteoric line. This behavior is consistent with the dominance of baseflow, with values most depleted appearing upstream and the most enriched being downstream as a result of slight evaporation from the course. The three samples in La Ballenera stream are closer to the global meteoric line, although greater enrichment is observed upstream. 222Rn concentrations were in the range of 1–2.5 Bq.L−1 in both. In the Vivoratá stream, 222Rn showed a tendency to increase in the downstream direction of the flow, while in the La Ballenera stream this trend was observed in the first two sections. CFCs values were significantly homogeneous at all sites. For most of the samples, the recharge year was set between 1987 and 1990, resulting in transit times in the order of 30 years. Combining field measurements of streamflow and EC, laboratory analyses of stable isotopes, CFCs and 222Rn, provides an efficient method for estimating groundwater discharge rates, which is ascertained by water apparent ages.

Impact of dairy farms on groundwater quality in a productive basin in the northeast of the Pampean Plain, Argentina

The Pampean Plain is a relevant world food production area where livestock and agricultural activities are developed. The northeast of this region is characterized by dairy production, where large quantities of excreta from the animals to the substrate cause environmental impacts associated with soil and groundwater contamination. On these dairy farms, the same water sources are used for animal nutrition, cleaning of facilities, and home consumption by rural workers. Groundwater quality assessment is therefore crucial to guaranteeing safe production and human supply. The aim of this work is to analyse the impact of family dairy farming on the geochemical processes that govern the groundwater quality of aquifers used for domestic and animal consumption in productive basins of the northeast Pampean Plain. An analysis of major ions, nitrates, and phosphates in groundwater was performed in 42 wells sampled at different periods. Also, sediments in diverse sectors were collected to be analysed for available phosphorus. The main point sources of contamination that were identified derive from farm facilities’ cleaning and the degradation of animal excrement. These sources infiltrate toward the unsaturated zone and reach the groundwater, or they directly enter through poorly constructed perforations. This produces reactions in the unsaturated zone, releasing protons and generating the dissolution of carbonates, increasing the groundwater hardness. The chemical compounds registered may produce limitations in water quality for human consumption and the development of agricultural activities, affecting animal nutrition and the production of a dairy basin in the northeast of the Pampean Plain.

SALINITY-RELATED PRESERVATION OF MOLLUSKS IN SHALLOW LAKES: IMPLICATIONS FOR THE UNDERSTANDING OF THE LACUSTRINE PAMPEAN FOSSIL RECORD

ABSTRACT Premortem and postmortem processes significantly influence the formation of the molluscan fossil record in freshwater environments. Despite their importance for paleoenvironmental studies, they remain poorly understood. In Pampean shallow lakes, Holocene shell deposits of the euryhaline snail Heleobia parchappii show a relation with salinity, as preservation seems to be favored by brackish-saline water conditions. To explore if this pattern may respond to ecological (i.e., differential survival and reproduction) or taphonomic processes acting differently in freshwater and brackish-saline environments, we conducted a field-based study comparing premortem (abundance, length, width/length ratio, and crushing resistance in living and dead shells) and postmortem (fragmentation, fine-scale surface alteration, and loss of periostracum of dead shells) attributes along a modern lacustrine salinity gradient (0.5–40 ppt) in the Pampa plain of Argentina. Snails from saline lakes were smaller and more rotund than those from freshwater lakes, exhibiting higher abundances and resistances in death assemblages. They showed the highest fidelity in shell length and the best states of preservation, which were similar to values recorded in fossil shells. We concluded that shells deposited in saline lakes are better preserved than those deposited in freshwater lakes, giving rise to highly abundant shell concentrations, analogues to those shell-rich fossil levels recorded in Pampean lakes. Such abundance does not reflect the natural abundances of living snails, but rather is the result of the combined influence that less destructive environments and better shell intrinsic properties have on preservation.

Pampa Plain (Argentina) Wetland History through a Lake Case Study: Kakel Huincul Environmental History during the Last 600 Years

Pampa Plain (Argentina) Wetland History through a Lake Case Study: Kakel Huincul Environmental History during the Last 600 Years

Nutrient dynamics in water resources of productive flatland territories in the Pampean region of Argentina: evaluation at a watershed scale.

The Pampean plains in South America are well-known for their livestock and agricultural productivity. The peri-urban watershed of El Pescado Creek (Central-Eastern Argentina) has been significantly modified in the last few years due to local land-use changes. This work aims to analyze the dynamics of nutrient content associated with the surface water-groundwater relationship in this watershed and to define the trophic state of the watercourse. Sampling sites were selected for both surface water and groundwater analyses, and field surveys were carried out during the spring and summer of 2017. Handmade shallow groundwater wells were installed along the floodplain of the watercourse. Deep groundwater was analyzed in agricultural and livestock farms. In situ determinations included dissolved oxygen (DO), pH, electrical conductivity (EC), turbidity, transparency, and temperature measurements. Laboratory analyses included NO3--N, total nitrogen (TN), soluble reactive phosphorus (SRP), total phosphorus (TP), and phytobenthonic and phytoplanktonic chlorophyll-a. Results showed an increase in EC and nutrient concentration in the summer samples (both in surface water and shallow groundwater), along with higher turbidity of the surface water. Water flow was dissimilar between samplings (spring: 1.735 m3/s, summer: 0.065 m3/s), showing contrasting hydrological scenarios. Low wash-out conditions enhanced phytobenthonic algae biomass growth, turning most of the sites towards a eutrophic state in summer. Our results showed that the dynamics of nitrogen and phosphorus compounds in the watershed of El Pescado Creek depend on the hydrodynamic processes of the watershed, the different land-uses, and the chemical characteristics of these compounds. In order to develop sustainable management strategies, further understanding of nutrient concentrations effects, and the factors affecting them, must be done in this area of the Pampean region.

Two different morphotypes of freshwater Cladophora surera (Cladophorales, Chlorophyta) produce similar sulfated cell wall polysaccharides

The Cladophoraceae (Cladophorales) includes branched (Cladophora) and unbranched (Chaetomorpha and Rhizoclonium) filamentous species, living in marine and freshwater environments. Species-level taxonomy is impeded by considerable morphological plasticity, related to environmental conditions, and switches between branched and unbranched morphologies have been reported within species. In this work, it was shown that Cladophora surera, a species widely distributed in streams in the Pampa Plains of Argentina, appears in two different morphotypes, branched and unbranched filaments. Phylogenetic analysis indicated that they correspond to the same species. The presence of these morphotypes could not be related with season or water flow. Moreover, under the same culture conditions it was possible to develop the branched morphotype from the unbranched one. The general structure of sulfated galactoxyloarabinans biosynthesized by the branched morphotype of this alga were studied previously. In this work, these sulfated 4-linked pyranosic arabinans were studied in relation to morphotype and season. It was shown that differences in structure of the water-soluble polysaccharides between samples could not be related to the morphotype but depend on the season. A detailed study by principal components analysis (PCA) of variables related with the main structural features showed clear differences between sulfated polysaccharides extracted from algae collected in spring, compared to those collected in other seasons. Structural analysis by chemical and spectroscopic methods of these sulfated arabinans collected in the different seasons are reported and discussed.

Dissolved silica dynamics, transfer and retention in a temperate groundwater flow-through shallow lake of the Pampean Plain, Argentina

Dissolved silica dynamics, transfer and retention in a temperate groundwater flow-through shallow lake of the Pampean Plain, Argentina

Strategic population responses of Daphnia spinulata Birabén, 1917 to salinity changes through laboratory bioassays

AbstractZooplankton play a key role in aquatic ecosystems constituting an essential intermediate component in aquatic food webs. Cladocerans in particular are widely studied as model of generalist filter feeders. At the regional level, the cladoceran Daphnia spinulata is found in numerous habitats with wide conductivity range (160 μS cm−1 to 14.000 μS cm−1), but information about the species's tolerance range or life history is scarce. Our objective was to generate essential information about D. spinulata's life history and the main parameters related to two contrasting salinity levels representative of water bodies of the pampean plain. Results obtained in laboratory bioassays showed that individuals at low conductivity (700 μS cm−1) had more moults, a lower mortality and a higher life expectancy at birth, a higher generation time, and an earlier peak density than those at high‐conductivity treatments (5000 μS cm−1). The maximum density reached was similar for both conductivities indicating a similar growth capability attained by different strategies. Moreover, the results indicated that D. spinulata at different conductivities was able to reproduce, with the offspring thus contributing to population growth. This study provided a knowledge of the life history strategies of this endemic cladoceran at two different conductivities, thus generating crucial information on the population dynamics and for evaluating the species's role as a possible salinity indicator in pampean water bodies. Nevertheless, future investigations will be necessary in order to identify the absolute limits of tolerance and the optimum conductivity for this species and determinate which stressors will act as a mictic stimuli.

Shallow lakes under alternative states differ in the dominant greenhouse gas emission pathways

AbstractOver the past decades, shallow lakes of the Pampean Plain, Argentina, have been shifting from clear vegetated to turbid phytoplanktonic states due to anthropic pressures. It is not clear, though, if this change in state also involves a change in the overall CO2 and CH4 balance of these lakes. Therefore, the main objective of this work was to assess potential differences in the C gas (CH4 and CO2) balance of shallow lakes under contrasting states—clear vegetated and turbid phytoplanktonic. We sampled two clear and two turbid shallow lakes in the Pampean region along an annual cycle and we measured all of the major C gas emission pathways: diffusive and ebullitive fluxes and also emissions from emergent vegetated habitats. CO2 and CH4 diffusive, ebullitive and vegetated habitat fluxes were comparable between states, but they differed in their relative contribution to the C gas balance because of differences in the coverage of the habitats associated to these pathways. Mean annual, area‐weighted CO2 and CH4 fluxes of clear lakes were 41.9 ± 19.0 and 15.4 ± 18.5 mmol m−2 d−1, respectively, and 7.7 ± 7.3 and 17.9 ± 19.8 mmol m−2 d−1 for CO2 and CH4 fluxes, respectively, for turbid lakes. Despite major differences in the relative contribution of the emission pathways between states, there was a remarkable convergence between states in total greenhouse gas emissions when expressed in terms of mean annual CO2 equivalent greenhouse gas flux.

Atrazine pollution in groundwater and raw bovine milk: Water quality, bioaccumulation and human risk assessment

Atrazine herbicide can bioaccumulate over time and thus affect humans for generations to come. However, scarce studies have evaluated its bioaccumulation potential in bovine milk, a nutritional staple for children and the elderly both domestically and internationally. This study aimed to determine its concentration in groundwater and bovine milk, as well as the risks it is likely to pose for human health. Eighteen dairy farms in the Pampean plain of Argentina were analyzed. A strong correlation was found between the chemical composition and the geomorphological characteristics of the plain. In addition, increased salinity was observed in the groundwater at greater distances from the aquifer's recharge area. Atrazine was quantified in 50 % of the groundwater samples (at values ranging from 0.07 to 1.40 μg/L), and in 89 % of the bovine milk samples (from 2.51 to 20.97 μg/L). Moreover, atrazine levels in 44.4 % of the groundwater samples and 11.1 % of the bovine milk samples (n = 18) exceeded the limits internationally established as safe for human consumption. The hazard quotient (HQ) values of the compound were negligible for children and adults, both in groundwater (child = 9.7E-4, adult = 4.5E-4) and in milk (child = 1.0E-2, adult = 1.6E-3). The estimated cancer risk (CR) values need further evaluation (child = 7.8E-6, adult = 3.6E-6 in groundwater; child = 6.6E-5, adult = 1.3E-5 in milk). In both types of samples, the HQ and CR of residual atrazine were higher for children than for adults. Nevertheless, bioaccumulation factors suggest that dairy cows have a moderate capacity to incorporate atrazine from abiotic matrices. This is the first report on residual atrazine in bovine milk in Argentina. The results presented here indicate that the status of atrazine contamination in the area should continue to be monitored in order to assess its long-term impact on public health.

Deciphering the environmental drivers throughout the 20th and 21st centuries in the paleolimnological record of Laguna del Plata, Laguna Mar Chiquita system, Northern Pampean plain, Argentina

Laguna del Plata (LP) is a small, shallow hypereutrophic saline lake which is part of the hydrological system of Laguna Mar Chiquita (LMC) (Córdoba, Argentina). Environmental variability of LP occurred in the last ca. 80 years, was reconstructed through a multi-proxy approach in LP-17-I sedimentary core.The synchronic correspondence of lithological units and physicochemical proxies throughout the paleolimnological record made it possible to identify two main environmental stages. Stage I (1934–1977 CE) records a long drought resulting in low water levels and high-water salinities, while stage II (1977–2017 CE) records a humid phase, high water levels and low water salinity. In stage II we distinguish three sub-stages related to changes in the nutrient load: sub-stage II A (1977–1983 CE), sub-stage II B (1983–2010 CE) and sub-stage II C (2010–2017 CE). Sub-stage II A is characterized by an increase in TN, carbonates, TOC, CD and TC, related to humid context and reduced water salinities rather than anthropic influence. During sub-stage II B, there is a synchronous increase of nutrients and primary production proxies which matches the urban population growth of Córdoba city and the expansion of the agricultural activity after the 1980s, during a favorable hydroclimatic context. During sub-stage II C, the increase of nutrient and primary production proxies was maintained, despite water lake level variability, as a consequence of anthropic influence. Results show that regional hydroclimatic variability can act synergistically with anthropic influence ruling the nutrient fluxes to LP and therefore influencing the eutrophication and primary productivity of the lake. However, our results allowed us to distinguish that stage I and sub-stage II A were mainly dominated by hydroclimatic variability while sub-stage II B and sub-stage II C were mostly governed by anthropic influence.This study contributes to the understanding of the role of natural and anthropic drivers on the environmental dynamics of the LMC hydrological system during the 20th and 21st centuries. These results provide tools for planning activities and improving watershed management policies in the Pampean plain region of Argentina.

Physical Factors and Microbubble Formation Explain Differences in CH4 Dynamics Between Shallow Lakes Under Alternative States

Submerged macrophytes play a key role in maintaining clear vegetated states in shallow lakes, but their role on methane (CH4) dynamics is less explored. They might enhance methanogenesis by providing organic matter but they can also supply oxygen to the sediments increasing methanotrophy. They may also affect gas exchange by diminishing wind turbulence in the water column. We previously measured seasonal CO2 and CH4 partial pressure (pCO2 and pCH4) and diffusive fluxes from two clear vegetated and two turbid algal shallow lakes of the Pampean Plain, Argentina, and we reported that clear lakes had higher mean annual pCH4 despite states having similar mean annual CH4 diffusive flux. In this study we explore the contribution of physical and biological factors regulating surface pCH4. Mean annual CH4 diffusive fluxes and CH4 fraction of oxidation (Fox) were similar between states, implying a comparable mean annual CH4 input. kCH4 was significantly higher than kCO2, suggesting occurrence of CH4 microbubbles, yet kCH4 was higher in turbid lakes than in clear lakes, implying a higher microbubble formation in turbid lakes. Furthermore, in turbid lakes there were positive relationships between k and wind speed, and between k and pCH4, yet in clear lakes these relations were absent. Results suggest that submerged vegetation suppresses wind induced turbulence in clear vegetated lakes, decoupling kCH4 from wind and reducing microbubble formation, therefore augmenting pCH4 in their surface waters. Overall, physical rather than biological factors appear to control the observed differences in pCH4 between states.