Blowout dynamics in lime‐rich and lime‐poor coastal dunes in the Netherlands

Blowouts can mitigate the negative effects of acidification in the topsoil, especially in industrialized countries with high atmospheric nitrogen (N) deposition. However, blowout activity may differ between lime-rich and lime-poor dunes, which creates different regional responses and interactions between processes and patterns. To further explore this, five Dutch dune sites were selected over the gradient from lime-rich and lime-poor dunes. We mapped blowout activity in 5 years between 1996 and 2017 with aerial photographs, and used transport potential, atmospheric N-deposition and rabbit density as explanatory variables. We also studied soil and plant parameters in the field in different stages of succession. All sites showed fluctuations, but blowout activity net increased in the lime-rich sites, and decreased in the lime-poor sites. Differences in blowout activity could not be explained by sand transport potential, which differed between years, but not sites. Differences in blowout activity could to some extent be explained by rabbit density and exceedance of the critical N load, although the transition site between lime-rich and lime-poor dunes showed high blowout activity despite low rabbit density. Differences in blowout activity between lime-rich and lime-poor dunes were also related to differences in topsoil chemistry, especially with respect to lime content, Fe content and different forms of phosphorus (P). High pH was a key factor, which reduced sensitivity to high N deposition through reduced P-availability to the vegetation, higher proportion of arbuscular mycorrhizal plants, which may improve food quality for rabbits, and lower root biomass, which may increase erodibility of the dune soil. High pH and low P availability may even occur in lime-poor dunes with a little lime, as long as blowouts stay active and counteract acidification. However, when pH values drop below 6.5, P availability to the vegetation will increase and start feedback processes leading to blowout stabilization.