The ecological potential of geotextiles in hydraulic engineering

Geotextile materials find increasing use in coastal protection as an alternative material to natural stone, slag, and concrete. In this environment geotextiles, like all surfaces of technical objects immersed in seawater, are subject to accumulation of organisms on their surfaces, a process usually called biofouling. In a 2-year experiment we investigated the colonization of benthic organisms on two different geotextile materials (woven fabric and non-woven fabric) in the Elbe estuary, Germany, and compared it with the colonization on unglazed ceramic tiles as reference representing the nearest compromise to natural hard substrates. Then, non-woven fabric was colonized by significantly less species, fewer individuals, and lower biomass values than the woven fabric and the ceramic tiles (one-factor ANOVA, p < 0.05); no such significant differences were noted between woven fabric and ceramic tiles. Over time, the numbers of species and numbers of individuals did not show significant increases between the first and the second year (Student’s t-test, p ≥ 0.05), while the biomass was still increasing significantly on all materials (t-test, p < 0.05). However, biomass was almost two orders of magnitude lower on non-woven geotextiles than on woven material. Exposure to seawater and fouling organisms had no adverse effect upon the stability of the geotextiles (wide-width tensile test results; t-test p ≥ 0.05). Geotextile materials therefore offer a unique choice in coastal and hydraulic engineering: depending on the application, engineers can choose between a material that is easily colonized by benthic species, or one that minimizes such colonization where it is undesired.