Small Headwater Lakes Research Articles

Message from the President: ASLO in the Time of Covid‐19

Message from the President: <scp>ASLO</scp> in the Time of Covid‐19

Eutrophication histories of three contrasting lakes in a naturally nutrient-rich boreal watercourse

The Iisalmi Route watercourse in central-eastern Finland contains a number of highly eutrophic lakes. Despite substantial impacts from anthropogenic activity, the region appears to be naturally eutrophic because of its geological setting. A passive continental ice sheet deposited fine-grained basal till that contributes to the naturally eutrophic status of the lakes. Detailed paleolimnological studies in the Iisalmi Route are few. Therefore, we studied the eutrophication histories of three contrasting Iisalmi Route lakes: (1) small headwater Lake Saarisjarvi, (2) larger, but very shallow headwater Lake Nalantojarvi, and (3) large central basin, Lake Porovesi. We compared the suitability of three diatom-total phosphorus transfer functions for application to fossil samples. A local transfer function, specifically targeted to the Iisalmi Route, was the most suitable for the headwater lakes. In contrast, two regional transfer functions, which have larger geographical coverage, performed equally well for the large central basin. All three lakes proved to have been naturally eutrophic for thousands of years. Highest natural variability occurred in the longest core, from shallow headwater Lake Nalantojarvi. This variability reflects the dynamic development of the basin and its catchment after deglaciation. Diatom assemblage changes in cores from Lakes Saarisjarvi and Porovesi suggest cultural eutrophication, most likely after the region was colonized in the sixteenth century, followed by salinization in more recent times. Our study deepens understanding of naturally eutrophic boreal lakes that are located on fine-grained tills and their sensitivity to natural and anthropogenic forcing. Our results also highlight the importance of selecting appropriate transfer functions and realistic restoration targets when dealing with naturally eutrophic lakes.

Physico-chemical changes in two northern headwater lakes in the Northwest Territories, Canada, during winter to spring seasonal transitions

Abstract This note describes extended monitoring of two small headwater lakes in the Lockhart River in the Northwest Territories (Canada) during consecutive late winter and spring transitions. During these transitions, the lakes changed from isolated ice-bound water bodies to interconnected lakes, throughout which they exhibited similar modifications to their physico-chemical characteristics. Lake temperature changes were linked to ambient conditions, with warming after May 1 initiating snow- and ice melt inflows. Lake temperatures of 3 °C to 4 °C were measured in both lakes at the start of monitoring, which were maintained until a steady increase commenced in early June 1 as ice cover started to recede. This period was also associated with peak water levels and lake discharges. Conductivity decreases (~ 26 to ~ 12 μS/cm in the larger, shallower lake, Area 8, to 16 to 11 μS/cm in the smaller, deeper lake, Lake I1) commenced around mid-May, in advance of lake temperatures increases, and stabilized after approximately 3 weeks once lake ice had melted. The extent of lake dilution based on conductivity decreases (54–56% in Area 8, and 31% in Lake I1) was attributed primarily to the ice cover melt volume on each lake at the start of monitoring. DO concentrations were mostly undersaturated at the start of the monitoring period, with values below aquatic life guidelines; Area 8 reached saturation once lake conductivity stabilized, but Lake I1 was saturated once conductivity started to decrease. pH transitioned from slightly acidic (~ 5.8; below aquatic life guidelines) to circumneutral, with the transition slightly different between lakes depending on the lake conductivity transition.

Spawning and rearing behavior of bull trout in a headwater lake ecosystem

Numerous life histories have been documented for bull trout Salvelinus confluentus. Lacustrine-adfluvial bull trout populations that occupy small, headwater lake ecosystems and migrate short distances to natal tributaries to spawn are likely common; however, much of the research on potamodromous bull trout has focused on describing the spawning and rearing characteristics of bull trout populations that occupy large rivers and lakes and make long distance spawning migrations to natal headwater streams. This study describes the spawning and rearing characteristics of lacustrine-adfluvial bull trout in the Quartz Lake drainage, Glacier National Park, USA, a small headwater lake ecosystem. Many spawning and rearing characteristics of bull trout in the Quartz Lake drainage are similar to potamodromous bull trout that migrate long distances. For example, subadult bull trout distribution was positively associated with slow-water habitat unit types and maximum wetted width, and negatively associated with increased stream gradient. Bull trout spawning also occurred when water temperatures were between 5 and 9 °C, and redds were generally located in stream segments with low stream gradient and abundant gravel and cobble substrates. However, this study also elucidated characteristics of bull trout biology that are not well documented in the literature, but may be relatively widespread and have important implications regarding general characteristics of bull trout ecology, use of available habitat by bull trout, and persistence of lacustrine-adfluvial bull trout in small headwater lake ecosystems.

Fish Community Response to a Small‐Stream Dam Removal in a Maine Coastal River Tributary

AbstractSedgeunkedunk Stream, a third‐order tributary to the Penobscot River in Maine, historically has supported several anadromous fishes including Atlantic Salmon Salmo salar, Alewife Alosa pseudoharengus, and Sea Lamprey Petromyzon marinus. Two small dams constructed in the 1800s reduced or eliminated spawning runs entirely. In 2009, efforts to restore marine–freshwater connectivity in the system culminated in removal of the lowermost dam (Mill Dam) providing access to 4.7 km of lotic habitat and unimpeded passage into the lentic habitat of Fields Pond. In anticipation of these barrier removals, we initiated a modified before‐after‐control‐impact study, and monitored stream fish assemblages in fixed treatment and reference sites. Electrofishing surveys were conducted twice yearly since 2007. Results indicated that density, biomass, and diversity of the fish assemblage increased at all treatment sites upstream of the 2009 dam removal. No distinct changes in these metrics occurred at reference sites. We documented recolonization and successful reproduction of Atlantic Salmon, Alewife, and Sea Lamprey in previously inaccessible upstream reaches. These results clearly demonstrate that dam removal has enhanced the fish assemblage by providing an undisrupted stream gradient linking a small headwater lake and tributary with a large coastal river, its estuary, and the Atlantic Ocean.

Rain Induced Changes in Carbon Dioxide Concentrations in the Soil–Lake–Brook Continuum of a Boreal Forested Catchment

The numerous water bodies and their riparian zones in the boreal zone are crucial to lateral carbon transport and can thus be very significant for carbon cycle on the landscape level. Therefore, we installed automatic measurement systems with Vaisala CARBOCAP CO2 probes (Vaisala Oyj, Vantaa, Finland) in the riparian zone soil matrix around a small headwater lake, in the lake itself, and in the outflowing brook and followed the seasonal and diurnal variation in CO2 concentration as well as rain event‐driven changes in this natural‐state soil–lake–brook continuum in Southern Finland. Seasonal variation was greatest and concentrations highest deep in the soil and in the lake, but were also noticeable in the brook. On the other hand, diurnal variation was highest in shallow soil layers and the lake surface. In the brook, the influence of the riparian zone superseded that of the lake at less than 150 m distance, which resulted in wider variation and higher concentrations of CO2. After the rain event, the normal diurnal pattern was changed, and the CO2 concentration in the soil increased as water filled the soil pores and slowed down the diffusion. Even though the water with lower CO2 concentration from the lake diluted the CO2 concentration in the brook, the input from the soil dominated the flow after the rain and concentrations increased. On an annual basis, the flow of terrestrial dissolved inorganic carbon (DIC) into the aquatic ecosystem was 1–13% of terrestrial net ecosystem production (NEP).

Discontinuities in stream nutrient uptake below lakes in mountain drainage networks

In many watersheds, lakes and streams are hydrologically linked in spatial patterns that influence material transport and retention. We hypothesized that lakes affect stream nutrient cycling via modifications to stream hydrogeomorphology, source‐waters, and biological communities. We tested this hypothesis in a lake district of the Sawtooth Mountains, Idaho. Uptake of NO3− and PO4−3 was compared among 25 reaches representing the following landscape positions: lake inlets and outlets, reaches &gt;1‐km downstream from lakes, and reference reaches with no nearby lakes. We quantified landscape‐scale hydrographic and reach‐scale hydrogeomorphic, source‐water, and biological variables to characterize these landscape positions and analyze relationships to nutrient uptake. Nitrate uptake was undetectable at most lake outlets, whereas PO4−3 uptake was higher at outlets as compared to reference and lake inlet reaches. Patterns in nutrient demand farther downstream were similar to lake outlets with a gradual shift toward reference‐reach functionality. Nitrate uptake was most correlated to sediment mobility and channel morphology, whereas PO4−3 uptake was most correlated to source‐water characteristics. The best integrated predictor of these patterns in nutrient demand was % contributing area (the proportion of watershed area not routing through a lake). We estimate that NO3− and PO4−3 demand returned to 50% of pre‐lake conditions within 1‐4‐km downstream of a small headwater lake and resetting of nutrient demand was slower downstream of a larger lake set lower in a watershed. Full resetting of these nutrient cycling processes was not reached within 20‐km downstream, indicating that lakes can alter stream ecosystem functioning at large spatial scales throughout mountain watersheds.

Recovery from acidification in boreal lakes inferred from macroinvertebrates and subfossil chironomids

Acidification of waters and soils caused by emissions and the long-range transport of air pollutants has been a serious worldwide problem during the last decades. The extent of the acidification problem in Finnish acid-sensitive forest lakes was examined in the Acidification Research Project (HAPRO) in the mid-1980s. The recent decline in the emissions of air pollutants has resulted in the chemical recovery of watersheds in many regions, and the present work on the recovery processes in acidified Finnish headwater lakes (REPRO) was launched to examine whether the chemical recovery has already been accompanied by biological recovery. The patterns of recovery were studied by re-sampling littoral macrozoobenthos in a subset of the previously sampled HAPRO lakes. Paleolimnological samples were taken in order to assess the possible dependence of lacustrine chironomid communities on the changing degree of acidification. Acid sensitive and moderately acid sensitive benthic species revealed slight recovery in the formerly most acidic (pH ≤ 5.5) but recently recovered lakes. The most significant factors affecting the response of benthic communities were increased mean lake pH and decreased labile aluminium concentration. Paleolimnological chironomid analysis revealed a slight response along the pH gradient, but also significant structural similarity between the present and pristine chironomid assemblages. This implies that no major changes in chironomid communities of these acidic lakes have occurred during the past centuries. The alternative future trends and threats to biological recovery in small headwater lakes are discussed.

Future recovery of acidified lakes in southern Norway predicted by the MAGIC model

Abstract. The acidification model MAGIC was used to predict recovery of small lakes in southernmost Norway to future reduction of acid deposition. A set of 60 small headwater lakes was sampled annually from either 1986 (35 lakes) or 1995 (25 lakes). Future acid deposition was assumed to follow implementation of current agreed legislation, including the Gothenburg protocol. Three scenarios of future N retention were used. Calibration of the sites to the observed time trends (1990–1999) as well as to one point in time considerably increased the robustness of the predictions. The modelled decline in SO4* concentrations in the lakes over the period 1986–2001 matched the observed decline closely. This strongly suggests that soil processes such as SO4 adsorption/desorption and S reduction/oxidation do not delay the response of runoff by more than a few years. The slope of time trends in ANC over the period of observations was less steep than that observed, perhaps because the entire soil column does not interact actively with the soilwater that emerges as runoff. The lakes showed widely differing time trends in NO3 concentrations over the period 1986–2000. The observed trends were not simulated by any of the three N scenarios. A model based on the C/N ratio in soil was insufficient to account for N retention and leaching at these sites. The large differences in modelled NO3, however, produced only minor differences in ANC between the three scenarios. In the year 2050, the difference was only about 5 μeq l-1. Future climate change entailing warming and increased precipitation could also increase NO3 loss to surface waters. SO4* concentrations in the lakes were predicted to decrease in parallel with the future decreases in S deposition. Fully 80% of the expected decline to year 2025, however, had already occurred by the year 2000. Similarly, ANC concentrations were predicted to increase in the future, but again about 67% of the expected change has already occurred over the past 20 years. The recovery of ANC was predicted to be incomplete. Even after the CLE scenario (for future acid deposition) is implemented, the chemical conditions in about one-third of the lakes were predicted to be insufficient to support trout populations in the future. Thus, additional measures will be required if these lakes are to be restored. Keywords: acid deposition, lakes, model, Norway, recovery

Distribution of woody debris in a small headwater lake, central Ontario, Canada.

The distribution of woody debris in the littoral zone of a small, oligotrophic headwater lake in south central Ontario, Canada was studied. Coarse woody debris (CWD) was defined as pieces of wood with a large-end diameter ≥10 cm and medium woody debris (MWD) as pieces of wood with a small-end diameter of 2.5 to 10cm. The mean length, diameter and volume of CWD was 530.4 cm, 17.3 cm and 181.9 dm 3 . For MWD, these parameters were 52.2 cm, 5.0 cm and 1.43 dm 3 , respectively. CWD was determined to be present at 1.18 pieces/m shore line occupying a volume of 0.212 m 3 /m shore line (0.0212 m 3 /m 2 ). MWD was estimated to be present at 24 pieces/m shore line occupying a volume of 0.034 m 3 /m shore line (0.0034 m 3 /m 2 ). There were significant correlations between the slope of the ecotonal lake bottom and number of CWD pieces found at each site and between water depth and volume of MWD, which suggests a trend for greater accumulation in steeper, deeper areas as opposed to shallower bays.

Predicting the long‐term acidification trends in small subarctic lakes using diatoms

Summary 1. A considerable proportion of the total deposition of sulphur in northernmost Europe originates from the large non‐ferrous smelters of the Kola Peninsula, Russia. Potential long‐term effects of this point source pollution on sensitive subarctic lakes were evaluated using palaeolimnological techniques. 2. Multivariate analysis of a diatom and water chemistry data set from 45 small headwater lakes located in north‐eastern Finnish Lapland demonstrated that pH, calcium and silica were the three most powerful chemical variables in explaining the variance in the diatom data. From these, lake water pH was shown to be the strongest determinator by variance partitioning. 3. Weighted averaging partial least squares regression (WA‐PLS) was used to develop a diatom‐based prediction model for inferring lake water pH from sediment core diatom assemblages. The performance of the model was assessed by leave‐one‐out cross‐validation. 4. The prediction model was applied to radiometrically dated sediment cores taken from three headwater lakes receiving different amounts of acid fallout from the Kola Peninsula smelter industry. 5. Stable diatom assemblages and results of pH reconstructions suggested that no substantial changes in the acidification status of the lakes have occurred within the last century despite the very high local acid deposition. 6. The pollution levels in the study area have not increased to the point where the biology of the lakes has been influenced significantly.

Impact of a Protective Limestone Treatment on the Water Chemistry and Zooplankton Community of Thrush Lake, Minnesota

AbstractA limestone slurry was sprayed on the surface of Thrush Lake, a small headwater lake in northeastern Minnesota, to test a treatment designed to protect acid‐sensitive waters from anthropogenic acidification. The 6‐year study, consisting of pretreatment, transition, and post‐treatment phases, was part of the four‐state Acid Precipitation Mitigation Program directed by the U.S. Fish and Wildlife Service. Measured water‐chemistry parameters, including acid‐neutralizing capacity, pH, dissolved calcium, and dissolved inoroganic carbon, increased following treatment, although local climatic conditions influenced the magnitude and duration of the chemical changes. Physical changes to the lake, other than an increase in conductivity and a short‐term alteration of water clarity subsequent to treatment, were not documented. The composition of the zooplankton community was altered, with the proportion of rotifers increasing after treatment. Individual zooplankton species showed a variety of changes in abundance that were associated with treatment over both seasonal and multi‐year intervals. For example, Holopedium gibbemm was absent from lake samples immediately following treatment and recovered within a season, whereas Diaptomus minutus and Keratella taurocephala populations were reduced after treatment and had not recovered by the end of the study. Alternately, Asplanchna priodonta increased in abundance after treatment. These observed abundance patterns were generally consistent with previzous acidification or base‐addition studies. In contrast, the changes in community composition of zooplankton did not consistently fit patterns developed from regional studies across water‐chemistry gradients. These differences emphasize the importance of biotic as well as abiotic factors in controlling zooplankton community composition.

Specific rates of net methylmercury production in lake sediments

Specific rates of Hg (203HgCl2) methylation and McHg (14CH3HgI) demethylation in aerobic and anaerobic conditions were determined in samples of surface sediments (0 to 2 cm) taken from five small headwater lakes in Southern Finland. The highest rates of methylation were measured in anaerobic conditions. However, the importance of aerobic methylation increased with increasing Fe and Mn content in sediment. There was little difference between aerobic and anaerobic demethylation. The results demonstrate that the net McHg production in lake sediments depends on the individual characteristics of the lake, particularly pH and and sediment properties. These characteristics seem to affect demethylation in anaerobic conditions and methylation in aerobic conditions.

Sources of mercury contamination in the sediments of small headwater lakes in south-central Ontario, Canada

To determine the significance of mercury contamination of remote lakes in three regions of south-central Ontario, Canada, sediment cores were collected at several stations in each of fourteen lakes. Profiles of Hg concentration with depth were similar to those found in many parts of the world and indicate a substantial increase in Hg loading to these lakes in recent decades. Surficial sediment concentrations (0–2 cm) ranged from 120 to 700 ng/g dry matter.

Zooplankton Diversity and Biomass in Recently Acidified Lakes

Ten small headwater lakes in the Adirondack Mountains of New York State and 10 in the White Mountains of New Hampshire were examined for possible effects of acidification on zooplankton. The results showed that acidification, or some close correlate, had a significant negative effect on zooplankton diversity and biomass. A loss of 2.4 species of zooplankton and 22.6 mg dry wt/m2 was correlated with each unit decrease in pH. These results, in contrast to some previous work, show a continuous decrease in diversity and biomass over the entire range of pH in the sampled lakes, 4.5–7.2. Cladocera, with the exception of Holopedium and Polyphemus, and Epischura lacustris, Mesocyclops edax, and Cyclops scutifer, were abundant at higher pH values but rare or absent at pH values less than 5. Diaptomus minutus was predominant at pH values less than 5.Key words: acid rain, lakes, Adirondack Mountains, White Mountains, zooplankton, Cladocera, Epischura, Mesocyclops, Cyclops, Diaptomus

Water Renewal Efficiency of Watershed and Lake Combinations in the ELA Region of the Precambrian Shield

Individual components of lakewater budgets in the Experimental Lakes Area (ELA) are highly variable through time. Direct field measurements combined with empirical relationships for unmeasurable components are required to achieve balanced lakewater budgets over short intervals of several hours or days. However, annual variations in the hydrological regime are related to a few simple characteristics of the lake and surrounding watershed. In the 1969–77 period the annual ratios of terrestrial evapotranspiration/precipitation and lake evaporation/precipitation showed little variation and were of a similar magnitude. As a result, the potential for water renewal or replacement in the lake basins annually can be characterized by only four factors: the annual precipitation, the tributary drainage basin area, the lake area, and the lake volume. The potential has been expressed as the Annual Watershed Efficiency (AWE), the reciprocal of the water renewal time, to obtain a linear relationship between the four variables. The AWE i a measure of the extent to which a particular watershed and lake combination can renew the lake water under various annual precipitation conditions. A general graphical relationship for the AWE has been prepared for small headwater lakes similar to those of the ELA for a range of annual precipitations.Key words: watershed hydrology, water renewal, water residence, precipitation/runoff ratios, water budgets, evaporation, watershed efficiency