Sandy beaches as Biocatalytical Filters

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Invisible life

Sandy sediments are the dominant type of the sea shore along the European coast. They are of prime importance for human recreation, tourism and coastal development, more people use sandy beaches than any other type of seashore. They provide the most productive fishing grounds, are major sources for a variety of raw materials (oil, gas and minerals). While the economic and social values of beaches are generally regarded as paramount, sandy shores also have special ecological features and contain a distinctive biodiversity that is generally not recognized. Beaches also provide unique ecological services, such as filtration of seawater. The intrinsic ecological values and functions of beaches are often perceived as secondary to their economic value. A possible reason is that the study of beach ecology is only now emerging as a theory-driven discipline. Due to the lack of quantitative data, permeable sands are not well represented in coastal management and monitoring programs, and public and policy makers are not aware of their importance. Consequently these environments and their resources are not protected sufficiently relative to their socio-economical value.

Biodiversity of sandy shore

Life between sand grains

Beaches (sandy beaches) are not just piles of sand, they are home to numerous species, they have important linkages with adjacent ecosystem. There is a full array of living organisms from bacteria, fungi, microphythobenthos, and protozoa to extremely specialized metazoan on the beach. Hundreds of species inhabit sandy beaches but most of them are small (less than a few mm) and buried. They occupy interstitial spaces between sand grains. These sandy beach dwellers exhibit remarkable physiological and behavioural adaptation to changing environmental conditions. Sandy beaches are dynamic and sensitive places where life is under pressure, practically without a break. Biodiversity provides many ecosystem services that are often not readily visible. It plays a part in regulating the chemistry of our atmosphere and water supply. Biodiversity is directly involved in water purification, recycling nutrients and providing fertile soils.

Permeable sediments

A key feature of sandy sediments is their permeability which means that water can flow through the interstices. The deflection of bottom water currents (due to tides, wind, or waves) by bottom topography (ripples, animal mounds, stones etc) creates horizontal pressure gradients at the sediment surface, which leads to advective flow of water through the sediment [1].[2][3].

Biogeochemical activity

Natural washing machine

As sediment light color reveals, organic mater and nutrient pools in near-shore sands are rather low, which led to the impression among scientists and coastal managers that these sediments are biogeochemically inactive. Recent investigations indicated that the contribution of permeable sands in the coastal cycles of matter may be underestimated[4]. Sand of coastal zone including sandy beaches may be as active as organic-rich fine-grained sediments, and fluxes of oxygen and nutrients can reach similar magnitudes, but high porewater transport rates in these permeable sediments limit depletion of oxygen and accumulation of solutes in the pore water[5]. „Sandy filtration” and ground water recharge lead to a good water quality A good water quality is reached by adsorption and precipitation processes. Self purification processes occur by the interstitial biocoenosis (meiofauna & -flora). Bacterial mineralization is of high significance for water quality.The contribution of living communities of sandy sediment to nutrient cycling and other ecological processes is probably substantial, but the details of such interactions are still poorly understood.

Who cares about microscopic beach crud? For one thing, anybody who likes to hang on the sand. This is the system that helps keep our beaches clean.


  1. Huettel, M. and Boudreau, B. 2000, Transport and reaction in permeable sediments. Coastal Ocean Processes Newsletter Issue 11: 3-5
  2. Huettel, M. et al 2002,Understanding the biocatalytical sand filter in the shelf. LOICZ Newsletter 25: 1-4
  3. Huettel, M. et al 2003, Coastal sands as biocatalytical filters (COSA. Coastline 12(1): 8-11
  4. Jahnke, R.A., Nelson, J.R., Marinelli, R.L. and Eckman, J.E. 2000, Benthic flux of biogenic elements on the Southeastern US continental shelf: influence of pore water advective transport and benthic microalgae. Continental Shelf Research 20(1): 109-127
  5. Shum, K.T. and Sundby, B. 1996, Organic matter processing in continental shelf sediments - The subtidal pump revisited. Mar. Chem. 53(1-2): 81-87

The main author of this article is Kotwicki, Lech Kotwicki