Spatial and temporal changes in species composition of submersed aquatic vegetation reveal effects of river restoration

We examined temporal changes in spatial patterns of submersed aquatic vegetation (SAV) in response to the restoration of geomorphic habitat in Navigation Pool 8 of the Upper Mississippi River from 1998 to 2016. The frequency of occurrence and species composition of SAV at sampling sites were spatially interpolated for each year to create annual maps. Linear models were fitted to temporal changes in SAV within each map pixel. The frequency of occurrence of SAV (across all species) increased over time in much of the impounded region of the pool, including areas near restored islands. However, impounded areas maintained a relatively consistent species composition over time, with species known to be tolerant of higher flow velocities (>0.10 m/second) and wind fetch distances (>1,000 m) (e.g. Vallisneria americana) being most abundant. In contrast, areas protected by newly constructed islands transitioned from V. americana to species found in other protected backwater habitats and known to be intolerant of high flow velocities and wind fetch distances (e.g. Ceratophyllum demersum). The results suggest that previously reported improvements in water clarity may have improved growing conditions for all SAV species, especially in the lower impounded portion of the pool, while island restoration created more backwater‐like habitats and facilitated changes in species composition. Assessing changes in SAV occurrence alone offers only a partial view of local‐scale river restoration (e.g. island building), while analyses of species composition are likely to be more indicative of the types of changes (i.e. reduced flow velocity and wind fetch) associated with restoring geomorphic habitat.     

Submerged aquatic vegetation correlations with depth and light attenuating materials in a shallow subtropical lake

A 3-year study was done to quantify the biomass of submerged aquatic vegetation (SAV) and its relationship with environmental attributes in Lake Okeechobee, the largest lake in the southeastern United States. Plants were sampled on 21 occasions at sites located along 15 fixed transects around the shoreline, giving rise to 721 observations of SAV species (Chara spp., Vallisneria americana, Hydrilla verticillata, Potamogeton illinoinensis) dry weight biomass. Environmental sampling focused on factors that attenuate light, including phytoplankton chlorophyll a (chl a), total suspended solids (TSS), non-volatile suspended solids (NVSS) and color. Depth and Secchi transparency also were measured. Based on regression analysis, NVSS was considerably more important in attenuating light than chl a or color. Total biomass of SAV varied from 0 to 271 g dw m^–2, with a mean of 4.7 g dw m^–2, and strong dominance by Chara. The SAV biomass was lower than average for Florida lakes, and may reflect the influence of suspended solids on underwater irradiance, as well as high water level in the late 1990s. Dense SAV was found only where depth was < 2 m and TSS < 20–30 mg l^–1. At locations where high biomass of SAV occurred, the plants may have influenced water quality, because concentrations of TSS, NVSS, and chl a were 2–3 fold lower than at sites with no plants. The potential effects of SAV also were apparent at a regional scale. The shoreline region of the lake displayed a pattern of rising and falling chl a and NVSS with water depth. This occurred both at sites with and without plants, suggesting that it may be driven by physical processes, such as water circulation patterns, which are influenced by depth. However, the pattern was dampened at sites with SAV, indicating a potential to influence these attributes of water quality.     

A Model to Estimate Potential Submersed Aquatic Vegetation Habitat Based on Studies in Lake Pontchartrain, Louisiana

The depth distribution of submersed aquatic vegetation (SAV) was studied in Lake Pontchartrain, Louisiana, to develop a model to predict changes in SAV abundance from changes in environmental quality. We conducted annual line‐intercept surveys from 1997 through 2001 and monitored monthly photosynthetically active radiation at four sites with different shoreface slopes. The following relationships between SAV distribution and environmental factors were used as model parameters: (1) water clarity controls SAV colonization depth; (2) fluctuation in annual mean water level and wave mixing determines SAV minimum colonization depth; and (3) site differences in SAV areal coverage under the comparable water quality conditions are due to shoreface slope differences. These parameters expressed as mathematical components of the model are as follows: mean water clarity determines SAV colonization depth (Z_max= 2.3/K_d); mean water level and wave mixing controls SAV minimum depth (Z_min= 0.3 m); and shoreface slope angle (θ) determines the distance from Z_min to Z_max. The equation developed for the potential SAV habitat (PSAV) model is PSAV = (2.3 ? 0.3 ×K_d)/(sinθ×K_d). The model was validated by comparing empirical values from the dataset to values predicted by the model. Although the model was developed to predict the PSAV in Lake Pontchartrain, it can be applied to other coastal habitats if local SAV light requirements are substituted for Lake Pontchartrain values. This model is a useful tool in selecting potential restoration sites and in predicting the extent of SAV habitat gain after restoration.     

Assessing the biomass and distribution of submerged aquatic vegetation using multibeam echo sounding in Lake Towada, Japan

Here we report on an advanced survey system that combines multibeam echo sounding with underwater photography, which was used to collect accurate data on the distribution and abundance of submerged aquatic vegetation (SAV) in Lake Towada. The use of this system enabled us to visualize the cover, height, and biomass of the SAV over the lake bottom, as well as to distinguish between different components of the SAV such as vascular and algal plants. The spatial distributions of these major components of the SAV varied as a function of the depth gradient. The vascular component was mostly represented by Potamogeton species, which accounted for around one-third of the standing mass of SAV, whilst more than half of the SAV was algal (charophytes). This abundance of charophytes may well be responsible for the high water quality and transparency of Lake Towada.     

Influence of migrant tundra swans (Cygnus columbianus) and Canada geese (Branta canadensis) on aquatic vegetation at Long Point, Lake Erie, Ontario

Numerous studies have shown that large, herbivorous waterfowl can reduce quantity of aquatic plants during the breeding or wintering season, but relatively few document herbivory effects at staging areas. This study was done to determine if feeding activities of tundra swans (Cygnus columbianus columbianus) and Canada geese (Branta canadensis) had a measurable additive influence on the amount of aquatic plants, primarily muskgrass (Chara vulgaris), wild celery (Vallisneria americana), and sago pondweed (Potamogeton pectinatus), removed during the fall migration period at Long Point, Lake Erie, Ontario. Exclosure experiments done in fall 1998 and 1999 showed that, as compared to ducks and abiotic factors, these two large herbivorous waterfowl did not have any additional impact on above or below ground biomass of those aquatic plants. As expected, however, there were substantial seasonal reductions in above-ground and below-ground biomass of aquatic plants in wetlands that were heavily used by all waterfowl. We suggest that differences in large- and small-scale habitat use, feeding activity, and food preferences between tundra swans and other smaller waterfowl as well as compensatory herbivory contributed to our main finding that large waterfowl did not increase fall reductions of Chara spp, V. Americana, and P. pectinatus biomass.     

Sediment resuspension and light attenuation in Peoria Lake: can macrophytes improve water quality in this shallow system?

We examined sediment resuspension and light attenuation in relation to the potential for macrophytes to improve water quality conditions in Peoria Lake, Illinois (U.S.A.). The lake exhibited high total suspended solids (TSS) loading and retention of predominantly fine-grained particles in 2000. Large fetches along prevailing wind rose, coupled with shallow morphometry and sediment particles composed of >90% silt and clay resulted in frequent periods of sediment resuspension. As calculated (wave theory) shear stress increased above the critical shear stress (measured experimentally), turbidity increased substantially at a resuspension monitoring station. Resuspension model explorations suggested that establishment of submersed aquatic macrophytes could substantially reduce sediment resuspension in Peoria Lake. However, K _d is currently very high, while Secchi transparency low, at in-lake stations. Thus, in order to establish a persistent macrophyte population in the lake to control resuspension, the underwater light regime will have to improve quite dramatically.     

Clear,crashing, turbid and back – long‐term changes in macrophyte assemblages in a shallow lake

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The effects of submerged aquatic vegetation on the persistence of environmental populations of Enterococcus spp.

Enterococcus spp. are utilized worldwide as faecal indicator bacteria, but certain strains exhibit extended survival in environmental habitats and the factors influencing their persistence are poorly understood. We used flowing freshwater mesocosms to explore the effect of submerged aquatic vegetation (SAV) on the persistence of natural enterococci populations from a subtropical lake. The highest mean densities of culturable enterococci over 2 weeks occurred in SAV [8.6 × 10² colony‐forming units (cfu) per 100 g wet weight], followed by sediments (1.3 × 10² cfu per 100 g) and water (18 cfu per 100 ml). However, due to relative differences in the total mass of each substrate in the entire system (water > sediments > SAV), SAV‐associated enterococci represented only a minor proportion of the total population. Vegetated mesocosms harboured significantly higher mean cfu per mesocosm and cfu densities in sediments compared with their unvegetated counterparts, suggesting that SAV indirectly facilitates persistence in aquatic habitats. Populations were dominated (> 96%) by a single Enterococcus casseliflavus strain according to BOX‐PCR genotyping, which did not change over the 10‐month study and strongly suggests bacterial replication in the lake. The presence of such strains in the environment may represent highly competitive, naturalized and reproducing indicator bacteria populations that are not directly related to pollution events.     

Growth dynamics of Potamogeton pectinatus L. in Lake Burullus,Egypt: a modelling approach

In this study, we used a macrophyte model to describe the growth production and the interaction between above‐ and below‐ground organs of Potamogeton pectinatus in Lake Burullus, Egypt. Above‐ and below‐ground biomass of P. pectinatus was sampled on a monthly basis from April to December 2011 at three sites of Lake Burullus. Shoots started to grow in April, reached the maximum biomass in September and then rapidly decreased in October when they moved into the senescence stage. Tubers biomass reduced in August due to the upward translocation to shoots, but sharply increased to the maximum in October by downward translocation from shoots and roots. Potamogeton pectinatus allocated approximately 82.3% of its total biomass to shoots, 15.5% to tubers and 2.2% to roots.     

Long- and short-term dynamics of submerged macrophytes in two shallow eutrophk lakes

1. Periods with clear water and abundant submerged vegetation have alternated with periods of turbid water and sparse vegetation during recent decades in Lake Tåkern and Lake Krankesjön, two shallow, calcium-rich, moderately eutrophic lakes in southern Sweden, Between 1983 and 1991, submerged vegetation (predominant species: Chara tomentosa, Nitellopsis obtusa, Myriophyllum spicatum) covered about 50% of the open lake area in Lake Tåkern. In Lake Krankesjön, submerged vegetation was sparse during 1983–84, but increased continuously in the following years and covered about 50% of the open lake area by 1990 and 1991. Potamogeton pectinatus was the first species to expand in Lake Krankesjön, but was later replaced by C. tomentosa. 2. During 1983–84, turbidity was high in Lake Krankesjön, which indicated that submerged macrophytes were light-limited. During 1986–91, there was a negative correlation between the areal coverage of charophytes and angiosperms, indicating that competition for space had become an important limiting factor. The same negative correlation was found in Lake Tåkern for 1983–91. 3. Charophytes had much higher biomass per unit area than angiosperms in both lakes and reduced water movement considerably. This was probably one reason for the increase of water transparency in Lake Krankesjön during the spatial expansion of these plants. Charophytes also stored large amounts of phosphorus and nitrogen, Charophytes are probably superior competitors for both space and nutrients and thus have competitive advantage over angiosperms in this lake type. 4. In Lake Krankesjön, both P. pectinatus and C. tomentosa were negatively affected by high water level during the growing period. Total disappearance of submerged vegetation occurred in both lakes after catastrophic events (dry-out during summer or mechanical damage by ice) caused by extremely low water level. Changes in water level are thus one of the most important reasons for among-year fluctuations in areal coverage of submerged macrophytes in these lakes.     

Post‐storm sediment burial and herbivory of Vallisneria americana in the Hudson River estuary: mechanisms of loss and implications for restoration

This article investigates the mechanics of loss of Hudson River Vallisneria americana after the high volume storms at the end of the 2011 growing season, when two severe weather events—Tropical Storm Irene and the remnants of Tropical Storm Lee—struck the Hudson River watershed. In 2012, the distribution of the most common species of submerged aquatic vegetation (SAV), Vallisneria americana (wild celery, water celery, or tape grass), in the Hudson River estuary declined by more than 90%, with no appreciable recovery in 2013 and 2014. Because of its important habitat value for aquatic life and for increasing dissolved oxygen, managers and scientists have begun discussing the reasons for the loss, as well as how to assist its recovery through assisted restoration efforts in the estuary. Supported by in situ and in vitro experiments, the article posits the hypothesis that sediment, washed into the river by the storm, buried overwintering tubers of the plant, thus reducing sprouting success. Sprouting was as low as 50% with sediment depth between 2 and 5 cm; sprouting did not occur with sediment depth greater than 10 cm. Field experiments found no support for the hypothesis that herbivory inhibited regrowth of the plant after the storm events. These results suggest that future assisted restoration of Vallisneria americana and SAV in general may require attention to system‐specific factors.     

Resistance to drought affects persistence of alternative regimes in shallow lakes of the Boreal Plains (Alberta,Canada)

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Komagataella populi sp. nov. and Komagataella ulmi sp. nov., two new methanol assimilating yeasts from exudates of deciduous trees

Two new species of the methanol assimilating ascosporic yeast genus Komagataella are described. Komagataella populi sp. nov. (NRRL YB-455, CBS 12362, type strain, MycoBank accession number = 564110) was isolated from an exudate on a cottonwood tree (Populus deltoides), Peoria, Illinois, USA, and Komagataella ulmi sp. nov. (NRRL YB-407, CBS 12361, type strain, MycoBank accession number = 564111) was isolated from the exudate on an elm tree (Ulmus americana), also growing in Peoria, Illinois. The species were resolved from divergence in gene sequences for domains D1/D2 LSU rRNA, ITS1-5.8S-ITS2, mitochondrial small subunit rRNA, RNA polymerase subunit 1 and translation elongation factor-1α. Species of Komagataella assimilate few carbon compounds and are unlikely to be resolved from differences in standard growth and fermentation tests. For this reason, separation of species is dependent on gene sequence analysis.     

The structure of population genetic diversity in <Emphasis Type="Italic">Vallisneria</Emphasis><Emphasis Type="Italic">americana</Emphasis> in the Chesapeake Bay: implications for restoration

Submersed aquatic macrophyte beds provide important ecosystem services, yet their distribution and extent has declined worldwide in aquatic ecosystems. Effective restoration of these habitats will require, among other factors, reintroduction of genetically diverse source material that can withstand short- and long-term environmental fluctuations in environmental conditions. We examined patterns of genetic diversity in Vallisneria americana because it is a cosmopolitan freshwater submersed aquatic macrophyte and is commonly used for restoring freshwater habitats. We sampled 26 naturally occurring populations of V. americana in the Chesapeake Bay estuary and its tributaries and found that the majority of populations have high genotypic diversity and are not highly inbred. Fourteen of the populations had high allelic and genotypic diversity and could serve as source sites for restoration material. However, substantial geographic structuring of genetic diversity suggests that caution should be used in moving propagules to locations distant from their source. In particular, we suggest that propagules at least be limited within four primary geographic areas that correspond to freshwater tidal and non-tidal, oligohaline, and seasonally mesohaline areas of the Chesapeake Bay.     

Long-term change in water transparency before and after the loss of eelgrass beds in an estuarine lagoon,Lake Nakaumi,Japan

Long-term changes in Secchi disk transparency in Lake Nakaumi, Japan, from 1932 to the present, which includes the periods before and after the loss of eelgrass (Zostera marina L.) beds, were compiled from previous reports. During the first (July 1932–February 1934) and the second (January 1949–November 1950) periods, the mean transparency was greater than 3 m at all observed stations. Data during the third period (July 1954–March 1956) are only available for the station at the center of the lake. The mean transparency during the third period was significantly lower than that of the second period but higher than the mean during the fourth period. This observation suggests that the decrease of transparency occurred during the third period. Because the decline of eelgrass beds in Lake Nakaumi occurred in the mid-1950s, the decrease of transparency most likely resulted from the shift in primary producers from submerged macrophytes to phytoplankton. Although the maximum transparency sometimes exceeded 3 m, mean transparencies during the fourth period (May 1975–December 2003) were less than 2 m at all stations, significantly lower than those during the first and second periods. The shift in the chief primary producer, from benthic macrophytes to phytoplankton, caused a subsequent shift in secondary producers. The opportunistic filter-feeding bivalve Musculista senhousia, regarded as a biofouling species of local fisheries, increased in Lake Nakaumi. The long-term monitoring data of transparency suggested that restoration of submerged aquatic vegetation may be indispensable for the remediation of the lake environment in this shallow eutrophic lagoon.     

The Role of Habitat and Herbivory on the Restoration of Tidal Freshwater Submerged Aquatic Vegetation Populations

Submerged aquatic vegetation (SAV) has declined precipitously throughout coastal areas and its reestablishment has long been an important objective of coastal management. We investigated restoration success of Vallisneria americana (wild celery) using seeds, seed pods, and whole shoot transplants at sites in the Chesapeake Bay in the United States where historical aerial photography has indicated that the species once grew. In addition, we evaluated habitat conditions and established herbivore exclosures to assess the impacts of water quality, sediment conditions, and grazers on planting success. Whole shoot transplants resulted in the most rapid cover of the bottom, but required greater planting effort. Direct dispersal of individual seeds was generally more successful than dispersal of intact seed pods, resulting in more rapid initial seedling growth. Overall, 100% bottom cover of whole shoot transplant plots could be reached in approximately 3 years, despite light attenuation coefficients (K_d) of 3.0 to 4.0. Transplants at shallow depths (<0.5 m) were able to rapidly grow and elongate to the surface at mid‐to‐low tidal heights. Transplants were successful in both muddy (8% organic) and sandy (<2%) substrates. Using mesh exclosures to protect the plants from herbivory was critical to restoration success. Although water quality and other habitat conditions are important for SAV growth and survival, restoration in the unvegetated areas studied here was limited by grazing of initial recruits. The establishment of protected founder colonies of sufficient size to withstand initial grazing pressures may be required to reestablish SAV in similar areas.     

Submerged vegetation development in two shallow, eutrophic lakes

Submerged macrophyte vegetation in two shallow lakes in the Netherlands, Lake Veluwemeer and Lake Wolderwijd, has been affected by eutrophication in the late 1960's and 1970's. Recent changes in the vegetation occurred in the period following lake restoration measures. Between 1987 and 1993, the dominance of Potamogeton pectinatus decreased, while Charophyte meadows expanded over the same time interval. The pattern of change of the dominant macrophyte species might result from changes in the underwater light climate. Seasonally persistent clear water patches associated with the Chara meadows have been observed in the last few years. The interaction between submerged macrophyte vegetation succession and water transparency in the lakes is discussed.     

A Century of Change in Macrophyte Abundance and Composition in Response to Agricultural Eutrophication

Clear Lake, Iowa, USA is a shallow, agriculturally eutrophic lake that has changed drastically over the past century. Eight macrophyte surveys since 1896 were pooled and examined to characterize long-term impacts of eutrophication on macrophyte community composition and relative abundance. Surveys in 1981 and 2000 revealed few submergent and floating-leaved species and a dominance in emergent species (Scirpus, Typha). Over the past century, however, species richness has declined from a high of 30 species in 1951 to 12 found today, while the community composition has shifted from submergent-(99%) to emergent-dominated floras (84%). Potamogeton praelongus was the first emergent species to disappear but was followed by several other clear water Potamogeton species. Several floating leaved and emergent genera increased in relative abundance with eutrophication, notably Nuphar, Nymphaea, Phragmites, Polygonum, Sagittaria, Scirpus, and Typha. P. pectinatus was present over the entire century due to its tolerance of eutrophic conditions. Macrophyte growth was generally light-limited, with 93% of the variance in relative abundance of submergent species explained by changes in water transparency. Clear Lake exhibits signs of alternative stable states, oscillating between clear and turbid water, coupled with high and low submerged species relative abundance. The maximum macrophyte richness occurred as the lake oscillated between submergent- and emergent-dominated states. Changes in the water level have also impacted macrophyte growth since the area of the lake occupied by emergent macrophytes was negatively correlated with water level. Strongest correlations indicated that macrophytes respond to water level variations with a 2-year time-lag.     

Effects of Submerged Aquatic Vegetation on Macrozoobenthos in a Coastal Lagoon of the Southwestern Atlantic

The freshwater‐dominated part of Rocha coastal lagoon recently experienced sudden colonization by submerged aquatic vegetation (SAV). Macrophytes may be beneficial or detrimental for the zoobenthos, and both assemblages may in turn affect the food availability for birds and fishes. With the aim of evaluating the effect of SAV on water conditions and on the composition, abundance and diversity of macrozoobenthos, vegetated areas (V, up to 500 g DW m^–2) were compared with vegetation‐free areas (N). The benthic abundance was higher in V (up to 5000 ind m^–2) than in N (up to 2200 ind m^–2). Species richness and abundance of amphipods, gastropods and chironomids were also higher at V compared with N. Conversely, the abundance of Tanais stanfordi (Crustacea), Erodona mactroides (Bivalvia) and Laeonereis culveri (Polychaeta), and the Shannon diversity were higher at N. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Coexistence and the comparative light relations of the submersed macrophytes Myriophyllum spicatum L. and Vallisneria americana Michx.

Summary The Eurasian watermilfoil (Myriophyllum spicatum L.) has partially replaced wild celery (Vallisneria americana Michx.) as a community dominant in the littoral zones of lakes of Madison, Wisconsin. The two species have very different growth forms, with that of M. spicatum corresponding more closely to the optimal growth form simulated by the macrophyte production model WEED. The objective of this research was to investigate the mechanisms by which Vallisneria could compensate for its nonoptimal growth form and coexist with Myriophyllum.A quantification of midsummer growth form for the two species at a rooting depth of 80–90 cm showed that M. spicatum had 68% of its shoot biomass within 30 cm of the surface, whereas V. americana had 62% of its leaf biomass within 30 cm of the bottom. Vallisneria had a light extinction coefficient ranging from 0.013 to 0.019 m²·g^-1, much higher than the value (ca. 0.006 m²·g^-1) for M. spicatum. This indicates less effective penetration of light to lower leaves of V. americana. Half-saturation constants describing the light-dependence of carbon uptake in shade and sun tissues ranged from 60–197 microeinsteins·m^-2·s^-1 for V. americana, and 164–365 einsteins·m^-2·s^-1 for M. spicatum. The optimum temperature for photosynthesis was 33.6°C for M. spicatum and 32.6°C for V. americana, but Myriophyllum was nearly twice as effective at carbon uptake at 10°C. Integration of all of the above features with WEED showed that, for midsummer conditions, V. americana more than compensated for apparently disadvantageous morphological features by its greater physiological adaptability to low light regimes. Coupled with the temperature-dependence of photosynthesis, it appears that V. americana is favored by midsummer conditions, whereas M. spicatum is at an advantage at other times.