Catchment Science – a good all rounder

Catchment monitoring
Equipment used in catchment science

Traditionally, in science, you chose your field in final year and that was where you stayed, for your career: once a zoologist, always a zoologist. As science has progressed, cross boundary disciplines have emerged. In Trinity we promote “two subject moderatorships” (TSM) where students can take two subjects in completely different disciplines, such as philosophy and maths. It is unsurprising then to see the interdisciplinary field of catchment science gather momentum – but what is catchment science?                                

Three years ago, I attended a lecture given by Brian Moss, hosted by the Zoological Society. Brian Moss is one of the world’s great freshwater scientists and has developed the notion that our freshwater systems (rivers, lakes, groundwaters) are the blood vessels of our earth. They connect fields to fields, states to states, and in some cases, countries to countries (River Danube, River Tiber… I could go on). Freshwater systems provide the life force that drives our economies – most of our daily processes would be impossible without water – and due to a lack of joined-up thinking, we are polluting them. The role of a catchment scientist is to look at a freshwater system with all of its inputs and outputs as a single entity. No longer are we just zoologists interested in the role of zooplankton, nor physicists interested in how sediment moves from field to river, nor only geographers interested in how humans have impacted the landscape; we must be all of these and more.

Taking the simple idea of a river catchment, you have the source (where the river starts) and the river moves towards an endpoint, usually the sea but in some cases a lake. All the processes, inputs and output that occur between these two points interest a catchment scientist. Figure 1 shows an agricultural river catchment conceptually, and what started out as a simple idea has now developed into a very complex situation.

Ag catchment
Fig. 1: Conceptual model of an agricultural catchment

When studying a catchment, you begin at the bottom and work your way up – i.e. what sort of bedrock is there? Does it hold any water? Previous blogs have centred on the role of submarine groundwater discharge and in a river catchment, this is no different. Groundwater provides water to the river during periods of low rainfall, comprising the baseflow, required to maintain the aquatic life in the river – but it may also carry contaminants accumulated from elsewhere in the catchment. Groundwater presence is detected by numerous methods, from pumping local wells to using resistivity and sonic sub-terrain surveying where changes in the signal indicate that water is below ground.

Then we move up one layer, and look at soils. Are the soils free draining, i.e. contaminants may move into groundwater easily? Or are they poorly draining so that once it rains, anything held on the surface may immediately move into the river or local surface drains? What type of soil is it? Some soils hold on to slurry and fertiliser well, reducing the amount moved to a freshwater systems and others have a much reduced nutrient uptake, increasing the likelihood of transfer of nutrients to the river. The type of soil may also indicate the type of agriculture present in the catchment.

Digital image
Algal growth indicating eutrophication
A rolling drumlin catchment in Co. Monaghan

Now to the surface layer, what a catchment scientist can see. Through the use of Google Earth, we can see agricultural activities long before we visit a catchment, depending on what time of year the photo is taken, of course. We also can acquire excellent datasets from Geological Survey Ireland (GSI) and the EPA, showing us the features of the catchment such as land use, soil type, bedrock and even where the river and its tributaries are located. We may also look at topography, available freely from some sources, where steeper hills will indicate a propensity for surface runoff (most likely carrying contaminants) while flat topography may indicate a very slow movement of nutrients and in some cases, areas of standing water.

When looking at the landscape, the catchment scientist will be interested in the interconnecting processes such as the network of stand-alone houses, all with individual septic tanks if far from mains supply, and the location of farm holdings which may contain slurry holding tanks, dairy parlours, and open manure stands, as well as roads, field drains, tributaries, and agricultural activities (grazing pasture as opposed to arable crop growing, fields used for hay as opposed to silage, and fields not used for anything at all!).

Slurry spreading on fields
The origin of said slurry spreading!

Finally, the catchment scientist needs to account for the human needs of the agricultural catchment. As we move towards Food Harvest 2020, farmers are intensifying their agricultural activities but they must do this within the constraints of the targets set by the Water Framework Directive. New practices and methods are often met with suspicion, and it may also be the job of a catchment scientist to persuade stakeholders that new technologies, practices and regulations are the best way to improve the quality of our freshwater systems.

Farmer's walk Dunleer
Farmers’ walk, Dunleer, Co. Louth

All of the above underpin the principle of source–pathway–receptor as first introduced by Haygarth et al. (2005). To improve the quality of the receptor (river, lake, humans, aquatic life), you may need to either remove the source (in Ireland we disallow the spreading of fertiliser and slurry on fields during late autumn and winter) or block/reduce the pathway that contaminants take to reach a river, such as installing buffer strips between fields and rivers or reed-beds to treat effluent from septic tanks. It is on these fundamentals that catchment science is based, everything is connected and everything has influence on everything else.

So there you have it, as a catchment scientist you need to have a good knowledge of geology, soil science, chemistry, physics, botany, zoology, and a dash of human economics as well. Do you have what it takes to be a catchment scientist – the good all-rounder?

Authored by Lucy Crockford, PhD student (and catchment scientist in the making), TCD Geography

Haygarth PM, Condron LM, Heathwaite AL, Turner BL, Harris GP. 2005. The phosphorus transfer continuum: Linking source to impact with an interdisciplinary and multi-scaled approach. Sci Total Environ, 344(1-3):5-14.

Thanks to John Kennedy and Tom O’Connell for providing some of the photos. Fig. 1 source: Ray Flynn (Senior Lecturer, School of Planning, Architecture and Civil Engineering, Queen’s University Belfast), pers. comm.



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