where k 1 is 0.00597 l · mol−1 · sec−1 and k3 = 0.456 l · mol−1 · sec−1 [51]. Because there is no empirical relationship between weight percent of carbonate and sediment porosity in tubeworm-dominated sediments [28], precipitation did not directly affect porosity. Precipitation was accounted for in the model by subtracting the volume of carbonate precipitate from the total volume encompassed by the rhizosphere.