Methods Manual for Salt Lake Studies/Putting it together - integrated biological approaches
Authors: PSJ Coleman,
- 1 Overview of integrated approaches to studying and monitoring salt lakes
- 2 A basic approach - daily monitoring solar salt-fields for biological health
- 3 Other integrated protocols
Overview of integrated approaches to studying and monitoring salt lakes
Around the world government agencies, researchers & community groups use combined monitoring approaches that measure chemical, physical and biological aspects of a habitat in order to assess the habitat's "health." Many of these approaches are described online. Well known combined monitoring approaches include protocols for fresh running waters (Barbour et al, 1999), freshwater lakes (Simpson, undated ) and estuaries (Orel & Register, 2002). Protocols for salt lake monitoring are not as easy to locate and so this chapter will endeavour to present several approaches to monitoring salt lakes.
A basic approach - daily monitoring solar salt-fields for biological health
Solar saltfields may appear, at first glance to be purely chemical facilities. However they support a distinctive biology that may impact on the production of salt for the benefit, or disadvantage, of the saltfield operator. Solar saltfield ponds are essentially a series of permanent saline wetlands and as such may exist in a range of ‘stable states’ or ‘ecological regimes’ (Sim et al 2006, Goldsborough & Robinson 1996)
In an ideal situation, the early ponds act as a brine purification wetland, removing nutrients and turbidity while the salinity is increased to the point where crystallisation occurs. At the other extreme the biology of the saltfield, fuelled by nutrients and disturbances, may give rise to an explosion of cyanobacteria that may produce a soluble slime that prevents the salt from crystallising (Coleman and White 1993, Roux 1996).
Monitoring saltfields biology can be a relatively expensive process for smaller operations and monitoring programs are frequently only initiated after a breakdown in field biology. Programs may be cut down, or discontinued, when conditions appear stable. As a result there may not be adequate warning of impending biological catastrophes.
Providing saltfield operators with tools to recognise the outward signs of the main saltfield pond ‘stable states’ can assist them in managing the biology of the field, and may provide them with advance warning that a closer examination of the field biology is called for.
So, which states are the ideal for solar salt production? Salt crystallises best from low viscosity, clean brines. Such brines are derived from series of ponds that have been maintained, in the majority of cases, in States 1 (lower salinity ponds) and 4a (higher salinity ponds). The image below provides a conceptual diagram that illustrates the visible aspects of each state. Click on the diagram to obtain a larger version.
What drives the change from one state to another?
Using the drivers as tools
The simplest tools to manage the biological aspects of a solar saltfield are to assess each pond to determine the most appropriate depth and salinity of brine, and then manage the flow of brine to maintain those two parameters within as narrow a band as possible. This aspect of pond control is an essential part of salt production, and extending the process to include management of the biology is usually relatively simple and economical.
Controlling input of nutrients to the solar saltfield may be simple, or complex. Diversion drains or levees may be needed to ensure surface water runoff from neighbouring agricultural activities does not enter the ponds. Managing the biology to reduce anaerobic events and other disturbances will ensure that nutrient loads are not passed from one pond to another. Where the feed water for the field is eutrophic, there may not be much the saltfield operator can do, other than support efforts of their local authorities to improve the situation.
Finally, biomanipulation may be called for. The three common classes of organisms added to a solar saltfield are herbivores (fish and invertebrates), filter feeders and predators. The first class reduces epiphytic algae and/or macrophyte loads in the ponds, allowing better light penetration and stronger macrophyte growth. Filter feeders such as brine shrimp reduce planktonic turbidity, while predatory fish control herbivore numbers or may be used to reduce the impacts of benthic feeding fish in a field.
What should saltfield operators look for (monitor)?
In the lower salinity ponds, the following are good indicators that the pond is maintaining State 1:
- the brine is clear and the pond bottom clearly visible
- extensive beds of seagrasses or widgeon grasses
- the leaves of the seagrasses are clean with no furry coatings
- there are no, or few, large tangles of fine hair-like green algae growing over the seagrass or widgeon grass beds
- herbivorous birds (e.g. black swans) are feeding on seagrasses and widgeon grasses
- fish eating birds (like pelicans) are actively hunting
In the higher salinity ponds, the following are good indicators that the pond is maintaining State 4a:
- the brine is clear and the pond bottom clearly visible
- any benthic mats are firmly attached to the pond bottom and are not showing signs of breaking up
- there are many brine shrimp visible
- there are flocks of small shorebirds feeding on the brine shrimp
Other integrated protocols
[More protocols, for specific types of lakes, targeting specific aspects of salt lake health, or looking in greater depth, would be welcome here]?