Pampean Shallow Lakes Research Articles

Variation in the area of the polymictic Pampean shallow lakes and its relationship with precipitation

Variation in the area of the polymictic Pampean shallow lakes and its relationship with precipitation

EXPERIMENTAL TAPHONOMY OF FRESHWATER DIATOMS: DISCRIMINATING BETWEEN CHEMICAL AND PHYSICAL CAUSES OF FRUSTULE FRAGMENTATION

ABSTRACT Frustule fragmentation is one of the major taphonomic factors affecting diatom preservation in Pampean shallow lakes. Although this has been demonstrated by taphonomic studies conducted on extant and fossil material, little is known about the causes of frustule breakage and its environmental significance. Field studies along modern environmental gradients showed a low but significant correlation between dissolution and fragmentation. Reworking of sediments by wind action has also been suggested as a plausible explanation for the fragmentation patterns observed in the field. To evaluate the relative importance of chemical and physical causes of diatom fragmentation, three laboratory experiments were conducted to test for (1) the effect of physical agitation; (2) the effect of chemical dissolution; and (3) the joint effect of both variables on diatom fragmentation. Diatom samples were subjected to physical agitation with a reciprocating shaker at 250 rpm for 20 days. Chemical dissolution was tested by mixing diatom assemblages with solutions of different concentrations of NaCl and NaHCO3, and pH 10 for 20 days. The joint effect of both processes was tested by dissolving diatom assemblages in salt solutions and subjecting them simultaneously to agitation for 20 days at 250 rpm. In all cases, aliquots of each assemblage were sampled at initial and final experimental times and their preservation analyzed via the application of fragmentation and dissolution indices. Significant and similar differences in fragmentation indices were observed in both dissolution alone and combined experiments, but no differences were found in samples subjected to agitation alone. In all cases, dissolution and fragmentation indices were correlated, suggesting a causal relationship between them. Overall, our results suggest that the debilitation of the diatom frustule by chemical dissolution may be the main cause of the fragmentation patterns observed in surface sediments of Pampean shallow lakes.

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.

Drivers of planktonic chlorophyll a in pampean shallow lakes

Although agricultural intensification has been linked with the increment of lake eutrophication and shallow lake research has demonstrated the importance of submerged macrophytes for maintaining water clarity, less is known about the role of macrophytes and the effects of agriculture on shallow lakes of the global south. Shallow lakes in the Pampean region of Argentina are subjected to high anthropic pressure and are classified as eutrophic and hypereutrophic and, in spite of most of them are turbid and dominated by phytoplankton biomass, some remain in a clear-vegetated regime with profuse submerged macrophytes. We studied the potential drivers of phytoplankton biomass (estimated as Chlorophyll-a - Chla) by applying a regional approach and a model selection process for a dataset of 58 shallow lakes that represent the variability of the Pampean region. For the 58 lakes, the presence of submerged macrophytes, total nitrogen, and nearby agriculture of each lake were the main drivers of Chla with −1.55, 0.19 and 0.02 coefficient values, respectively. Moreover, a high proportion of the variance in this dataset (37.7 %) was explained by the regional location of each lake (hydrographic systems). For lakes with macrophytes (N = 8), Chla exhibited a positive relationship with total phosphorus (coefficient value = 3.05), whereas for lakes without macrophytes (N = 50) Chla showed a positive relationship with nearby agricultural development (coefficient value = 0.02) and 36.4 % of variance explained by the hydrographic system. Our regional approach highlighted the importance of submerged macrophytes in shaping phytoplankton biomass in Pampean shallow lakes. Our results support the idea that the conservation of submerged macrophytes, as well as the control of agriculture in the riparian zones of lakes, will help to stabilize the shallow lakes in clear regime, even in regions highly impacted by agriculture and in lakes under eutrophic conditions.

Estructura y dinámica del bacterioplancton en cuatro lagunas pampeanas de la cuenca del río Salado (Buenos Aires, Argentina)

Bacterioplankton is an essential component for the functioning of aquatic ecosystems and has a profound impact on the water quality of the aquatic environments. It is therefore important to increase knowledge about its dynamics and genetic diversity. The main objectives of this work were to evaluate the structure and dynamics of bacterioplankton from four Pampean shallow lakes located in the upper (Gómez and Carpincho) and lower (Chascomús and El Triunfo) basins of the Salado River, as well as to determine the influence of environmental factors on these communities. To achieve this, seasonal samplings were performed during one year (January 2015-January 2016), in which main limnological variables were determined and the structure of bacterioplankton was analyzed by means of Illumina next-generation amplicon sequencing of the 16S rRNA gene. Bacterioplankton diversity indices were significantly higher in shallow lakes from the upper basin relative to those of the lower basin. Bacterioplankton richness was significantly lower in the clear-regime and disconnected shallow lake (El Triunfo) than in the turbid-regime and connected shallow lakes (Gómez, Carpincho and Chascomús). Bacterioplankton composition differed between all shallow lakes, except between the nearby and interconnected shallow lakes (Gómez and Carpincho). Environmental variables, such as total phosphorus, conductivity and Secchi depth, influenced the bacterioplankton composition in the studied lakes. Similarity in the bacterioplankton composition increased significantly with higher environmental similarity between lakes and decreased with spatial distance between them. Our results showed the bacterioplankton structure of the studied lakes was ruled by environmental and spatial factors. The bacterial structure varied between basins, and also between systems with different regimes and/or connections to the river.

The limnological trace of contemporaneous anthropogenic activities in the Pampa Region

Shallow lakes are the most productive freshwater ecosystems in the Argentinian Pampa Region. Only in Buenos Aires province, about 14000 shallow lakes larger than 10 ha exist, which provide important ecosystem services. Since the middle XX century profound changes are occurring in the region as a consequence of the anthropogenic activities, mainly associated to the expansion of agriculture, but also to livestock and urbanization. Different studies strongly suggest that changes in land use, as well as increased eutrophication of lakes, accelerated since 1990’s. In this article, we provide a general overview of the main features of the Pampean shallow lakes and a review of published evidences based on paleolimnological and satellite images studies that indicate changes in the state of the lakes related with eutrophication during the last two centuries. On the other hand, we analyzed the historical changes that are occurring in these systems since the 1980’s until the present by means of the principal variables associated with trophic status. This analysis, based on a data set of 740 samples from 87 shallow lakes, showed that nutrients (TP and TN) and algal biomass (as chlorophyll a) increased over the time, whereas transparency (Secchi depth) decreased; differences between XX and XXI centuries were significant. We also evaluated the change in the cyanobacteria assemblages (abundance and composition) between both centuries. We found that the biomass of this group increased in the XXI century and the composition of the assemblages changed, which nowadays are frequently represented by potentially toxic, bloom forming species. The shallow lakes of the region play an important role as sentinels of changes and all pieces of evidence are showing the impact of the anthropogenic activities.

Factores ambientales condicionantes del metabolismo de una laguna pampeana

Pampean shallow lakes naturally have water nitrogen and phosphorous concentrations that allow the development of dense beds of submerged aquatic vegetation, phytoplankton, or free-floating aquatic plants. In recent years, the eutrophication of these shallow lakes has increased due to the intensification of agriculture, use of fertilization and livestock. Phytoplankton- induced turbidity inhibits the growth of the submerged aquatic vegetation leading to phytoplankton dominance. This is the case of the Lobos shallow lake, which in a period greater than 20 years has remained as an organic turbid shallow lake, with cyanobacteria dominance. The study of the ecosystem metabolism can give relevant information about how the trophic state of a shallow lake drives production, respiration and net metabolism, and the potential consequences for aquatic biota. We evaluated the Lobos shallow lake metabolism using diel changes in dissolved oxygen concentrations during autumn and spring. Gross primary production showed lower values and variability in Autumn (1.57±1.33 g O2.m-2.día-1) than in Spring (20.45±18.00 g O2.m-2.día-1). Although there was high production during the day, respiration was also high, especially in Spring, where there was higher density of planktonic organisms principally cyanobacteria, exceeding net production in both seasons. Thus, we found mainly low or negative values for the net metabolism in Lobos shallow lake. A high oxygen consumption occurred during spring and at the lowest depth, coinciding with the highest chlorophyll-a concentrations, particulate matter, and lowest water transparency. We conclude that Lobos shallow lake was predominantly heterotrophic during study period. High nutrient concentrations will likely increase the factors that produce stress and negative impacts on aquatic fauna.

Drivers of Planktonic Chlorophyll a in Pampean Shallow Lakes: A Regional Approach

Drivers of Planktonic Chlorophyll a in Pampean Shallow Lakes: A Regional Approach

Response of shallow lakes in the arid-semiarid Pampas of Argentina to Late Holocene hydroclimatic change

This study presents a paleolimnological and paleoclimatological reconstruction based on diatoms and phytoliths of four Pampean shallow lakes (from south to north, La Salada, Sauce Grande, Los Chilenos, and Puan) strategically located along a climatic gradient from arid (south) to semiarid conditions (north). This research aims to identify the main drivers and mechanisms of long-term ecological change, and the main climatic mechanisms behind the regional hydroclimatic variability. It was found that these lakes were initially temporary, with clear waters, and eventually, became permanent with turbid waters. We propose that this change is due to an increase in precipitation in the last ca 1000 years, which resulted in higher lake levels and an increase in surface area, leading to an increased fetch and subsequent resuspension of sediment. This climatic amelioration occurred after ∼910 cal yr BP, first in what is today the arid Pampean region, then in the semiarid region, and finally in the modern humid region at ∼ -9 cal yr BP (1959 CE). Variations in lake's water level were the main driver of ecological change, followed by salinity (in Puan and La Salada) and nutrient load (in Los Chilenos and Sauce Grande). In general, those lakes on the southwest, located closer to the limit of moisture influence originating in the Pacific and Atlantic oceans (Arid Diagonal) were more sensitive to hydroclimatic changes than those located in the central Pampean region.

Human impacted shallow lakes in the Pampean plain are ideal hosts for cyanobacterial harmful blooms

The ecological status of Pampean shallow lakes is evidenced by Cyanobacteria Harmful Blooms impairing these nutrient enriched, turbid and polymictic water bodies spread along the Central Plains of Argentina. Under the premise that shallow lakes are sentinels of global climate and eutrophication, a 3-year research in ten lakes located across a climatic gradient explored which factors drove the dynamics of cyanobacterial assemblages frequently driving to bloom prevalence. Contrarily to what is expected, the effect of seasonal temperature on cyanobacteria was subordinated to both the light environment of the water column, which was on turn highly affected by water level conditions, and to nutrient concentrations. Monthly samplings evidenced that cyanobacterial assemblages presented a broad-scale temporal dynamics mostly reflecting inter-annual growth patterns driven by water level fluctuations. Both species composition and biovolume gradually changed across a gradient of resources and conditions and hence, the scenario in each individual lake was unique with patterns at different temporal and spatial scales. More than 35 filamentous and colonial morphospecies constituted the assemblages of Pampean lakes: nostocaleans and chroococcaleans were inversely correlated in the prevailing interannual 3-cycled patterns.

The performance of ecological cage aquaculture of pejerrey Odontesthes bonariensis in Pampean lakes under two different hydrological scenarios

Ecological aquaculture promotes the development of sustainable farming systems, focusing on a wide range of ecosystem elements. The ecological aquaculture of the zooplanktivorous pejerrey (Odontesthes bonariensis) in floating cages in Pampean shallow lakes (Argentina) needs to be carried out considering the hydrological and chemical variations as modulators of plankton community and consequently of the pejerrey yield. To assess its performance in lakes with contrasting hydrological regimes, an experiment was carried out in two water bodies: La Salada de Monasterio Lake (Mon), an endorheic environment, and San Lorenzo Lake (Lor), connected to several lakes and the Salado River. During the experiment, regional rainfall generated high hydrological variability in Lor Lake changing its status of unconnected lake to a run-of-the-river lake. High standard deviation in Chlorophyll-a values in Lor indicated the significant effects of hydrological instability on the plankton community. Microcrustaceans abundance and biomass were higher in Mon, and almost disappeared in Lor when it turns into run-of-the-river. The final fish growth and survival were significantly higher in Mon, endorsing the importance of zooplankton of high nutritional quality and hydrological, physical–chemical and biological stability. The results indicate that productive and stable environments with a sustained offer of natural food are better for the zooplanktivorous fish production. Connectivity with other water bodies and hydrological dependence on rainfall regimes have defining effects on phytoplankton, zooplankton and fish production, thus emerging as key factors to be considered for achieving better results in the ecological aquaculture implementation.

Effect of land use on the phytoplankton community of Pampean shallow lakes of the Salado River basin (Buenos Aires Province, Argentina)

The Salado River basin, Buenos Aires, Argentina, contains numerous permanent shallow lakes under anthropic pressure due to different land uses/land covers (LULC) in their catchments. Here, we explored the relation of LULC in the surrounding areas and the physical and chemical variables of six shallow lakes of the aforementioned basin with phytoplankton structure and morpho-functional groups (MFGs) along one year and evaluated whether LULC or physical and chemical variables were more relevant in shaping phytoplankton structure. We hypothesized that: (1) shallow lakes with higher proportion of land committed to agriculture exhibit more eutrophic characteristics; (2) the phytoplankton structure and MFGs differ in shallow lakes with different LULC in their surrounding areas; and (3) LULC effects decrease with increase in buffer width. Landsat satellite images were used to extract LULC composition in three buffer zones surrounding each lake: 1, 2.5 and 5 km. In all the lakes studied, LULC had greater influence on phytoplankton MFGs than physical and chemical variables. This influence was highest for the 2.5 km buffer. The phytoplankton structure and some physical and chemical characteristics were also different between the shallow lakes studied. Cyanobacteria were widely detected, probably related to the high proportion of land dedicated to agriculture in the region. Chlorococcales, typical of these eutrophic systems, were also well represented. Our study evidenced the influence of LULC on the shallow lakes studied, particularly on the phytoplankton structure. The response of the planktonic microalgal communities to human activities in catchments evidences their value as sentinels of aquatic ecosystems.

Connectivity of temperate shallow lakes to groundwater in the Pampean Plain, Argentina: A remote sensing and multi-tracer approach

The Pampean Plain in Argentina is one of the most extended plain regions of the world with numerous wetland systems and very shallow lakes. Certain anomalies related to geomorphology and shallow lakes’ hydrology are particularly present in a sector of the southern Pampean Plain, specifically, in the southwestern limit of the Quequén Grande River Basin. Here, shallow lakes can be defined as upland-embedded wetlands, characterized by the lack of observable hydrological connectivity due to the absence of surface water flows. The aim of this study was to identify groundwater connectivity of Pampean shallow lakes considered as upland-embedded wetlands and classify them according to their water presence frequency over time and their water source origin based on natural tracers (18O–H2O, 2H–H2O, electrical conductivity and Cl− content). In this work, a methodological framework involving a multitemporal analysis of the Normalized Difference Vegetation Index (NDVI) and the Normalized Difference Water Index (NDWI) derived from Landsat data, in addition to field data is proposed. According to water presence frequency, shallow lakes were classified in four categories: occasionally (89.0 %), regularly (6.7 %), usually (1.9 %) and permanently (2.3 %) with water. Obtained results allowed identifying shallow lakes having low, moderate or high mineralized water due to both different evaporation degree and water sources.

Effects of polyphenols on plankton assemblages and bacterial abundance representative of a pampean shallow lake: an experimental study

Shallow lakes are complex environments that play an important role in ecology. Their relationships with the surrounding areas make these lentic water bodies susceptible to alterations in response to human activity. For example, the input of polyphenols could be critical in altering species interactions. The shallow lakes located in the pampean plain of Argentina are major reservoirs of diversity, with the environmental habitats of the Salado River basin in particular having become impacted by human activities. The aim of this work was to evaluate the effects of different polyphenol concentrations (i.e. tannins) on changes in the plankton assemblages and on the abundance of bacteria in San Miguel del Monte Lake. Factorial experiments under laboratory conditions (4 tannin concentration levels and 4 response times) revealed that high tannin concentrations affected neither the phyto- and zooplankton assemblages nor bacterial abundances. Major changes both in assemblages and in the bacterioplankton abundances were dependent on exposure time. We found that the initial food web of grazers shifted to detritivorous feeding, thus producing a simplification of the community toward early succession. Although no effects of polyphenols were registered here, what proved striking was the resilience of the system and the capability to support high tannin concentrations throughout the experiment. Therefore, future investigations are necessary to elucidate the key role of such humic substances in the structuring of plankton assemblages of shallow lakes from strongly impacted areas, such as those found in the pampean region.

Covariation patterns of phytoplankton and bacterioplankton in hypertrophic shallow lakes.

The aim of this work was to assess the temporal patterns in the community composition of phytoplankton (PCC) and bacterioplankton (BCC) in two interconnected and hypertrophic Pampean shallow lakes in Argentina. Factors shaping their community dynamics and community temporal covariations were also analysed. We performed 4 years of seasonal samplings (2012-2016) and communities were studied by the Utermöhl approach (PCC) and Illumina MiSeq sequencing (BCC). We found marked seasonal variations in both communities and inter-annual variations with decreasing microbial community similarities during the study. We also observed covariation in community-level dynamics among PCC and BCC within and between shallow lakes. The within-lake covariations remained positive and significant, while controlling for the effects of intrinsic (environmental) and extrinsic (temporal and meteorological) factors, suggesting a community coupling mediated by intrinsic biotic interactions. Algal-bacterial associations between different taxa of phytoplankton and bacterioplankton within each lake were also found. PCC was mainly explained by pure regional extrinsic (17-21%) and intrinsic environmental (8-9%) factors, while BCC was explained by environmental (8-10%) and biotic interactions with phytoplankton (7-8%). Our results reveal that the influence of extrinsic regional factors can be channeled to bacterioplankton through both environmental (i.e. water temperature) and phytoplankton effects.

THE CHIRONOMIDS (DIPTERA: CHIRONOMIDAE) OF SHALLOW LAKES OF THE HUMID PAMPA REGION, ARGENTINA: AN APPROACH TO PALEOPRODUCTIVITY RECONSTRUCTION

ABSTRACTThe Humid Pampa, center-east of Argentina, is the most important socio-economical area of the country. Several shallow lakes have been the focus of many studies due to the significant changes in their trophic status related to human activities and to global warming recorded since the beginning of the twentieth century. Although chironomids have been used extensively in paleoclimatic and paleoenvironmental research, they are rarely used for paleoenvironmental reconstructions of the Pampean shallow lakes. The aim of this paper is to contribute to the knowledge of the chironmids' community composition and distribution in the Pampa region, and to relate their distribution to selected climatic and limnological variables. The ultimate goal is to retrieve new ecological information for future paleoenvironmental and paleoclimate reconstructions by using chironomid-based inference models. In this study, chironomids head capsules were collected from surface sediments from 17 shallow lakes of the Humid Pampa. Our analyses indicate that the chironomid assemblages reflect the decreasing NE-SW rainfall gradient of the region as well as the land use intensity, which in turn affects the aquatic ecosystems, in terms of lake productivity. Some chironomids are associated with brackish conditions (e.g., Chironomus, Ablabesmyia, Tanytarsini D2). Additionally the occurrence of assemblages of detritivore taxa such as Goeldochironomus, Chironomus, Polypedilum, and Dicrotendipes reflect the natural eutrophic state of Pampean shallow lakes, whereas assemblages mostly dominated by Coelotanypus, Procladius, and Chironomus are indicative of hypertrophic conditions, which are usually the result of human activity. This is the first study of chironomids from surface sediments from the central temperate plains of Argentina, and our records extend the ecological information of the Diptera in temperate areas. Although more studies are necessary to fully understand the main factors determining the chironomid fauna distribution in the Pampa region, we conclude that chironomids are potentially good proxies for paleoproductivity and salinity reconstructions of Pampean shallow lakes.

Zooplankton hatching from dormant eggs in a large Pampean shallow lake

Dormancy is an essential component of the life cycle for populations that disappear from the plankton during winter. The hatching of resting eggs is the main mechanism for restoring active population components. Here, we analyzed the hatching dynamics of zooplankton from sediments of a shallow lake as affected by temperature. Sediment samples collected every other month were incubated at in situ temperatures and at 20°C. The highest number of individual's hatchings was observed for copepod nauplii, the cladoceran Bosmina sp., and the rotifer Brachionus havanaensis. Temperature showed a positive significant effect on the hatchlings of B. havanaensis. Other zooplankton species were less affected by temperature, and there was no relationship between their emergence from the incubated sediments and occurrence in the water column. We also tested the effect of short-term (6 and 12 weeks) and long-term (a year) storage duration on hatching success. The hatching success of B. havanaensis was not affected by the storage time. In contrast, the hatchlings of Bosmina sp. and nauplii increased after short storage time. The evidence collected here suggests that many zooplankters were not affected by temperature, while for B. havanaensis temperature turned out to be a master variable that links planktonic and passive phases.

Spatial and temporal dynamics of the mesozooplankton (Crustacea: Cladocera, Copepoda and Decapoda) in a Pampean shallow hyposaline lake during drought conditions

The Sauce Grande Lake, a shallow, eutrophic, and hyposaline lake, was studied through monthly samplings during a year (December 2009- November 2010). The drought that affected the region since 2009 and during the entire study period interrupted the regular inflow from the river and outflow to the Atlantic Ocean. The lake presented an increase of salinity values and highly turbid conditions as a result of the drought conditions and wind resuspension. Small cladocerans such as Moina micrura and the copepod Boeckella poopoensis dominated the mesozooplankton community. The salinity determined the mesozooplankton composition; meanwhile, the abundance dynamic was ruled by temperature in conjunction with the eutrophic conditions during the study period. In a global context of climate change, and in a region where drought and wet cycles are frequent, these results further contribute to understanding the processes affecting the zooplankton community structure and dynamics during extreme climate events.

Factors that control the seasonal dynamics of the shallow lakes in the Pampean region, Buenos Aires, Argentina

Shallow lakes are distinctive aquatic ecosystems of the Pampean region. In this paper, climatic, morphometric and chemical-environmental aspects of six lacustrine bodies of the Salado River basin, Buenos Aires, are analyzed. The climatic variability of the region was estimated and linked to the behavior of each water body during the studied period (2017–2018); precipitations displayed deviations from the mean values, with periods of deficit in spring and summer, and excess in autumn. The analysis of satellite images showed a group of lakes with very low variation of the morphometric parameters because they have gates that keep the water level constant. On the contrary, those without anthropic intervention displayed a greater morphometric variability, since the water levels have been directly linked to local weather fluctuations. From a chemical-environmental perspective, changes were observed both at the regional (p = 0.015) and local (p = 0.0014) levels. Differences among sites cannot be characterized by a single variable but by a set of them. The dominant cation in the Pampean shallow lakes is the Na+ coming from the contact of groundwater with loessic sediments. Lakes showed a particular anionic dominance that not following a seasonal but a particular pattern. These are mainly linked to the characteristics of the substrate (presence of marine sediments or gypsum deposits). The great vulnerability of these environments to global and regional climatic changes, anthropic modifications and a large number of shallow lakes in the area, allow finding different scenarios (geomorphological, ecological, hydrogeological, etc.) to assess their vulnerability and predict their behavior against future climate scenarios in an economically important area for Argentine.

Assessing the Influence of Saline and Alkaline Environments in the Preservation of Pampean Diatoms: An Experimental Approach

Diatom dissolution is controlled by environmental conditions prevailing during fossilization. In Pampean shallow lakes, diatom dissolution showed important correlations with gradients of salinity, pH, carbonate, and bicarbonate, being these the most probable causes of the observed shifts in Holocene assemblages preservation. In the present contribution, a series of experiments were conducted in order to demonstrate the effect that physical-chemical lake characteristics exert on Pampean diatom assemblages preservation. Three experimental assemblages were subjected to the effect of three concentrations of two salts, NaCl (0.6, 1.2 and 3M) and NaHCo3 (0.6, 0.9, and 1.2M), and two pH values (7 and 10). Aliquots of the experimental solutions were removed once each five days for 20 days, and analyzed for changes in dissolved silica concentration (SiDi), relative and absolute abundances of diatoms, and dissolution indices (DDI) based on the target taxon Cyclotella meneghiniana. All the experimental solutions increased the SiDi significantly, particularly since day 10. These increased SiDi values were accompanied by significant changes in the DDI, which reached maximum values at pH 10, and by evidence of dissolution observed in SEM images, whereas no significant changes in relative or absolute abundances of diatoms were registered. These experimental results demonstrated the impact that water chemistry can exert on diatom dissolution in Pampean shallow lakes, even during short-term exposures. Given the naturally high pH, NaCl and NaHCo3 concentrations characteristic of many of these lakes, these experimental findings can be confidently extrapolated to the interpretation of the dissolution trends found in modern and fossil sedimentary assemblages.