Summary
1. All heavy metals, including those that are essential micronutrients (e.g. copper, zinc, etc.), are toxic to algae at high concentrations.

2. One characteristic feature of heavy-metal toxicity is the poisoning and inactivation of enzyme systems. Many of the physiological and biochemical processes, viz., photosynthesis, respiration, protein synthesis and chlorophyll synthesis, etc., are severely affected at high metal concentrations.

3. Some algae inhabit waters chronically polluted with heavy-metal-laden wastes from mining and smelting operations; Nodularia sp., Oscillatoria sp., Cladophora sp., Hormidium sp., Fucus sp. and Laminaria sp., etc., occur in metal-rich waters. These algal forms are probably more capable of combating the toxic levels of heavy metals and this attribute is a result of physiological and/or genetic adaptations. The sensitivity or tolerance to heavy metals varies amongst different algae. The phenomena of multiple tolerance and co-tolerance may be exhibited by some algae.

4. Heavy-metal pollution causes reduction in species diversity leading to the dominance of a few tolerant algal forms. The primary productivity also decreases after metal supplementation.

5. The uptake and accumulation of heavy metals can be active (energy-dependent), passive (energy-independent), or both.

6. Heavy metals can be safely stored as intranuclear complexes by some algae. Notwithstanding this, some changes in the cell wall can enable the algae to tolerate heavy metals by checking the entry of the metals (exclusion mechanism).

7. The metal content of algae growing in a waterbody may yield valuable information for simulating heavy metal pollution: several species of Cladophora and Fucus have been extensively used for this purpose.

8. Several factors affect and determine toxicity of heavy metals to algae. At low pH, the availability of heavy metals to algae is greatly increased, as a consequence of which pronounced toxicity is evident. Hard waters decrease metal toxicity. Some ions, e.g., calcium, magnesium and phosphorus, can alleviate toxicity of metals.

9. The presence of other metals can influence toxicity of a heavy metal through simple additive effect or by synergistic and antagonistic interactions. Similarly, other pollutants can influence heavy-metal toxicity.

10. The toxicity of heavy metals depends upon their chemical speciation. Various ionic forms of a metal characterized by different valency states, may be differentially toxic to a test alga.

11. Amino acids, organic matter, humic acids, fulvic acid, EDTA, NTA, etc. can complex with heavy metals and render them unavailable. This may eventually lead to less toxicity.

12. Heavy-metal toxicity largely depends upon algal population density: the denser the population the more numerous the cellular sites available, leading to decreased toxicity.

Phycology and heavy-metal pollution

https://www.floatingwetlandsolutions.com/pdfs/Tanner%20Headley%20Latest.pdf

Components of floating emergent macrophyte treatment wetlands influencing removal of stormwater pollutants

(1980). Environmental Factors that Influence the Toxicity of Heavy Metal and Gaseous Pollutants to Microorganisms. CRC Critical Reviews in Microbiology: Vol. 8, No. 2, pp. 99-145.

Environmental Factors that Influence the Toxicity of Heavy Metal and Gaseous Pollutants to Microorganisms

Three common Appalachian plant species (Juncus effusus L., Scirpus validus L., and Typha latifolia L.) were planted into small-scale constructed wetlands receiving primary treated wastewater. The experimental design included two wetland gravel depths (45 and 60 cm) and five planting treatments (each species in monoculture, an equal mixture of the three species, and controls without vegetation), with two replicates per depth planting combination. Inflow rates (19 L day 1 ) and frequency (3 times day 1 ) were designed to simulate full-scale constructed wetlands as currently used for domestic wastewater treatment in West Virginia. Influent wastewater and the effluent from each wetland were sampled monthly for ten physical, chemical and biological parameters, and plant demographic measurements were made. After passing through these trough wetlands, the average of all treatments showed a 70% reduction in total suspended solids (TSS) and biochemical oxygen demand (BOD), 50 to 60% reduction in nitrogen (TKN), ammonia and phosphate, and a reduction of fecal coliforms by three orders of magnitude. Depth of gravel (45 or 60 cm) had little effect on wetland treatment ability, but did influence Typha and Scirpus growth patterns. Gravel alone provided significant wastewater treatment, but vegetation further improved many treatment efficiencies. Typha significantly out-performed Juncus and Scirpus both in growth and in effluent quality improvement. There was also some evidence that the species mixture out-performed species monocultures. Typha was the superior competitor in mixtures, but a decline in Typha growth with distance from the influent pipe suggested that nutrients became limiting or toxicities may have developed.

Treatment of domestic wastewater by three plant species in constructed wetlands

http://retina.umh.es/docencia/metodologia/TrabajosAmbientales/1078.pdf

pH-dependent toxicity of copper and uranium to a tropical freshwater alga (Chlorella sp.).

Effects of copper, zinc and cadmium on Selanastrum Capricornutum

Influence of aquatic macrophytes on phosphorus and sediment porewater chemistry in a freshwater wetland

Changes in benthic macroinvertebrate population density and diversity were studied in a mesotrophic lake with seasonal hypoxia/anoxia prior to and following aluminum sulfate (alum) treatment and hypolimnetic oxygenation. Historically, low oxygen concentrations created a benthic zone with reduced fish predation pressures which allowed chaoborids to flourish. Population densities of chironomids and oligochaetes were suppressed by prolonged periods of summer anoxia Benthic macroinvertebrate community diversity values were indicative of poor water quality and/or habitat quality. Following alum treatment and prior to hypolimnetic oxygenation, chaoborid densities doubled. This was due, in part, to changes in trophic structure which provided an abundant food source for early instar chaoborids. In addition, Newman Lake was stocked with fewer trout in 1990 and 1991 resulting in reduced predation on the invertebrate community. Alum treatment had no effect on chironomid or oligochaete populations. Hypolimne...

Habitat Availability and Benthic Invertebrate Population Changes Following Alum Treatment and Hypolimnetic Oxygenation in Newman Lake, Washington

Hypolimnetic aeration is a widely used technique for lake restoration and fisheries enhancement. However, system design still depends on application of “safety factors” to observed oxygen demand rates, in large part because actual oxygen demand may be greater after aeration than before. Laboratory incubations of sediment show that sediment oxygen demand (SOD) rates follow mixed order kinetics, with an initial period of zero order reaction, followed by first order kinetics. The transition from zero to first order kinetics may correspond to the transition from laminar to turbulent flow. This suggests that SOD reaction kinetics are governed by thickness of the diffusive sublayer adjacent to the sediments. Therefore, zero and first order reaction regions correspond with oxygen diffusion limitation and substrate limitation, respectively. Such a mechanism would account for the induced oxygen demand observed following hypolimnetic aeration and would reconcile differences in SOD reaction orders noted in the literature. This paper describes development of equations based on laboratory SOD incubations for predicting induced oxygen demand following hypolimnetic aeration.

a Model for Predicting Lake Sediment Oxygen Demand Following Hypolimntetic Aeration

Giffin Lake is a shallow, eutrophic lake in south central Washington and the sub ject of an intensive Phase I restoration diagnostic/feasibility study. Water quality problems in the lake have been manifested principally as excessive growth of the floating-leaved macrophyte, Nymphaea odorata, white water lily. Study results indicate that these macrophytes play a central role in chemical, physical, and biological functioning of the lake. The extensive macrophyte canopy prevents diffusion of oxygen to the sediments by inhibiting both gas exchange with the atmosphere and transfer of wind energy to the water column. Anaerobic conditions develop under the summer macrophyte canopy, as do steep nutrient gradients. Phytoplankton seasonal distribution appears to be strongly influenced by competition with macrophytes for nutrients and light. Zooplankton communities are dominated by rotifers which can tolerate low oxygen conditions and which feed on bacteria and detritus prevalent beneath the macrophytes. Fi...

William H. Funk

Papers

Effects of copper, zinc and cadmium on Selanastrum Capricornutum

Influence of aquatic macrophytes on phosphorus and sediment porewater chemistry in a freshwater wetland

Habitat Availability and Benthic Invertebrate Population Changes Following Alum Treatment and Hypolimnetic Oxygenation in Newman Lake, Washington

a Model for Predicting Lake Sediment Oxygen Demand Following Hypolimntetic Aeration

Water Quality, Fishery, and Biologic Characteristics in a Shallow, Eutrophic Lake with Dense Macrophyte Populations