BOTANY WITH THE BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

XIII. PLANT INDICATORS OF SURFACE WATERS

Various elements of the Earth's hydrosphere are closely linked to the vegetation cover. Therefore, plant indicators can be used in The Study of sea and ocean waters, inland surface waters, snow cover, and groundwater.

When studying surface waters, botanical indicators are used to characterize the aquatic environment of permanent and temporary Water bodies, as well as surface runoff from watersheds.

Ocean, sea, and lake areas. The composition and distribution of benthic and planktonic vegetation in seas and lakes serve as indicators of illumination, Temperature, chemical composition, organic matter mass, water mass movement, and ice regimes [31, 120, 131]. Plankton acts as an indicator of the hydrological state and origin of waters, while benthos indicates the average hydrological regime of bottom layers over a long period [38].

The vertical distribution of submerged vegetation reflects the decrease in illumination with depth. Along the Black Sea coast, in the upper sublittoral zone from 0 to 3–5 m with an illumination of 100000-80000 lux, the most sciaphilic or light-demanding species (polyphotes) predominate: flowering plants such as Zostera, green Algae (Ulva lactuca, Cladophora and Enteromorpha species) mixed with brown algae (Dilophus repens, Padina pavonia) and red algae (Ceramium ciliatum, Polysiphonia opaca) [38]. The middle sublittoral zone, from 3–5 to 10–15 m in depth with an illumination of 40000-20000 lux, is occupied by moderately light-demanding algae (mesophotes), predominantly brown algae: Cystoseira barbata, Dilophus fasciola, Nereia filiformis, Zanardinia prototypus, with an admixture of the red alga Ceramium rubrum. Finally, in the lower sublittoral and elittoral zones at depths from 10–15 to 50–60 m, where illumination drops to a few hundred lux, only shade-loving (umbrophilic) red algae are widespread—Phyllophora nervosa, Dasya pedicellata, Polysiphonia elongata—along with the brown alga Ectocarpus siliculosus and others. The depth range of polyphytic and mesophytic algae allows for an assessment of water transparency.

Many algae exhibit a specific, narrow temperature range (stenothermy); therefore, they can be used as indicators of particular thermal properties of water. For instance, the cryophilic alga Phaeocystis pouchetii, with an ecological minimum of 1.0° C, an optimum of 6° C, and a maximum of 11.6° C, is a characteristic indicator of cold polar waters [31]. Cold-hardy species of the genera Fucus, Bangia, Enteromorpha, as well as thermophilic algae of the genera Trichodesmium and most Syracosphaera, occur exclusively in warm waters at temperatures around 20° C. Typical representatives of tropical waters include benthic brown algae of the genera Sargassum and Sphacelaria, as well as species of Siphonaceae and Lithothamnium.

Salt-tolerant organisms are closely associated with the degree of water mineralization. The euglenoid alga Halosphaera viridis, for example, avoids insufficiently saline waters (below 30°/oo). Saline marine waters are characterized by communities of brown and red algae of the genera Fucus, Cystoseira, Laminaria, and Macrocystis. An Abundance of algae indicates mesohalobious conditions with a salinity ranging from 3 to 30°/oo. Many algae serve as indicators of fresh or slightly mineralized waters (up to 3%), such as Rhizosolenia longiseta and Spirogyra species. Due to the varying sensitivity of algae to salinity, their distribution characterizes changes in waters of different mineralization degrees. In Norwegian fjords, with a drop in salinity, Fucus serratus disappears first, followed by F. vesiculosus and F. sherardi, with F. ceranoides being the last to disappear [98].

The planktonic "mosaic" also reflects the distribution of waters with varying salinity. Diatom algae have proven to be sensitive indicators of chloride content in saline waters [131]. Polyhaline diatoms—Nitzschia ovalis and Navicula longirostris—indicate a Cl content of 60–80 g/L, while Nitzschia frustulum is distributed at a Cl concentration of 30–50 g/L. A large number of mesohaline algae are known—Amphora commutata, Nitzschia apiculata, Melosira nummuloides—which serve as indicators of Cl content ranging from 7 to 20 g/L (group a) or from 2 to 6 g/L (group b).

Finally, Cyclotella meneghiniana and Thalassiosira fluviatilis serve as indicators of low salinity (Cl up to 2 g/L).

In lakes, plants are also used as indicators of The chemical properties of water (saturation with organic matter, salinity by readily soluble salts). In freshwater lakes of the humid zone of the European part of the Russian Federation, eutrophic waters saturated with humic compounds and Mineral Substances are accompanied by rich littoral vegetation including Oenanthe aquatica, Phragmites communis, Carex lasiocarpa, Menyanthes trifoliata, as well as floating plants such as Nuphar luteum and Nymphaea candida, and submerged plants like Sagittaria sagittifolia and Sparganium simplex. Oligotrophic waters, which are the purest and poorest in organic matter, are characterized by a specific vegetation consisting of Isoetes lacustris, Sparganium affine, Littorella sp., and Lobelia sp. Dystrophic waters, saturated with humic compounds, acidic, and poor in mineral substances, are typical of boggy forest and Sphagnum peatland areas. In nutrient-poor water bodies, the first littoral zone is formed by Equisetum fluviatile, Carex acuta, and green mosses, which are further replaced in the water by zones of pondweeds, water smartweed, and bur-reed. In arid-zone lakes, plants serve as indicators of water mineralization. In the lakes of Northern Kazakhstan, Sagittaria sagittifolia, Nymphaea candida, and Stratiotes aloides act as indicators of fresh waters (Polyakov, 1952). Other plants are widespread in saline lakes (exceeding 1 g/L): Myriophyllum verticillatum, Nymphoides peltata, Potamogeton compressus, and others.

The Study of the vertical distribution of algae provides an opportunity to characterize changes in temperature and salinity. While conducting hydrobiological studies in Lake Mogilnoye (coast of the Kola Peninsula), S.O. Zernov [31] discovered that freshwater algae of the genera Rivularia, Enteromorpha, and Cladophora inhabit the upper layers (0–5 m), whereas the polyhaline red alga Phyllophora brodiaei grows abundantly at a depth of 8–13 m. Such vertical ecological compatibility indicates the two-layered Nature of the waters: fresh on top, saline at the bottom. An example of thermal stratification is the composition and distribution of Algae in the White Sea [35]. Thus, in the upper, relatively warm water layers (around 10° C), boreal species such as Fucus vesiculosus, Laminaria saccharina, and Ceramium rubrum are widespread. Deeper than 20 m, in colder horizons dominated by lower temperatures, they are replaced by cryophilic arctic species: Polysiphonia arctica, Ceratocolax hartzii, and Phyllophora interrupta.

Specific features in the distribution of marine algae characterize the direction and intensity of sea currents. The appearance of a thermophilic flora in cold locations indicates the presence of warm currents. For instance, the spread of the thermophilic alga Halosphaera viridis in the cold Kara Sea allows researchers to trace the warm Branches of the North Cape Current [31]. Conversely, the appearance of cold-loving algae in middle latitudes indicates the penetration of cold polar waters. For example, off the western coast of Southern Africa, cold-hardy species of the genera Laminaria and Macrocystis are used as indicators of the cold Benguela Current waters [125].

In addition to anomalies in the distribution of stenothermic species, Conclusions regarding the Movement of water masses are facilitated by studying the geography of algae with varying degrees of halobiosy. Freshwater algae are distributed far from the sea coast—off the deltas of large rivers (Congo, Amazon) and small rivers (Umba River) [39]—where runoff currents freshening the saline marine waters are characteristic. Conversely, polyhaline species penetrate brackish seas along with oceanic waters (Atlantic branches in the North Sea, etc.).

Helland-Hansen and Gran established in 1902 that many planktonic organisms are excellent indicators of sea currents. The consistent development of these ideas led to the study of North Sea plankton and the compilation of a planktonic "mosaic" reflecting the genetic composition of waters [119, 131]. The authors identified a series of hydrological regions and defined so-called key indicator forms for each.

The Development of aquatic vegetation indicates the vertical movement of water masses. Downwelling currents accompanying strong flows lead to improved aeration and salt regimes in deep layers, as well as the "submergence" of vegetation zones. An indicator of such phenomena is the spread of large Phaeophyceae to greater depths near the Orkney Islands and along the Pacific coast of North America [120]. The upwelling of deep waters and the enrichment of surface layers with nitrates and phosphates are associated with areas of the most abundant phytoplankton development off the coasts of Algeria and the Arabian Peninsula [31]. In polar waters, conversely, the minimum amount of phytoplankton marks the upwelling of cold waters to the surface, while the maximum marks the sinking of warm layers to depth [38].

In arctic regions, the composition of phytoplankton can be used as an indicator of the ice regime of seas [38]. In these seas, algal development begins the moment the surface is freed from ice. Consequently, the stage or degree of plankton development indicates the duration of the "open" sea period. The mass development of "spring" species, predominantly diatoms with a high chlorophyll content, indicates recent ice melting—about 15–20 days prior. Furthermore, "early spring" diatoms—Thalassiosira gravida, Achnanthes taeniata, Fragilaria oceanica, F. islandica—develop During the first decade, while "late spring" species—Chaetoceros socialis, Ch. furcellatus—develop In the second decade after the sea surface clears. This massive "spring bloom" of the ocean depletes the main nutrient reserves in the water and is subsequently replaced by an aspect dominated by peridinians with a minor quantity of diatoms. The indicator of a prolonged (at least one month) ice-free water period is the mass development of "summer" plankton with a low chlorophyll content—Peridinium pellucidum, P. brevipes, etc., mixed with colorless diatoms such as Nitzschia seriata and Chaetoceros mitra.

Littoral-aquatic and submerged vegetation can be used as an indicator of hydrodynamic conditions in the water areas of lakes, rivers, and reservoirs [13].

In reservoirs and large rivers with weak water currents (up to 0.05-0.07 m/s) under moderate wave action, bands of plant communities with diverse compositions develop: lakeshore bulrush (Scirpus lacustris), broadleaf cattail (Typha latifolia), yellow water-lily (Nuphar luteum), spiked water-milfoil (Myriophyllum spicatum), and others. In areas with rapid currents (0.07-0.20 m/s), only pure stands of common reed (Phragmites communis) remain, alongside submerged species such as floating pondweed (Potamogeton fluitans) and marsh calla (Calla palustris).

The presence of littoral-aquatic vegetation stands indicates a significant weakening of wave impact on the shore. For instance, medium-density reed beds attenuate waves by 4–7% per 1 meter of width, while high-density beds reduce them by 20% and decrease the magnitude of dynamic wave pressure on the shore by up to 60%. Several rows of shrubby willows (Salix triandra, S. cinerea) completely dampen waves 0.5–0.6 m high and higher. The wave-protection role of trees is significantly lower.

Stands of submerged plants impede water movement within the channel. Under otherwise equal conditions, aquatic plants reduce the water flow velocity by 25% or more compared to the velocity in a vegetation-free section of the river.