diff --git a/core/src/parameter.jl b/core/src/parameter.jl
index 97bc1cab3..48a58e4a0 100644
--- a/core/src/parameter.jl
+++ b/core/src/parameter.jl
@@ -266,10 +266,6 @@ for discrete control
     itp_update::Vector{ParameterUpdate{ScalarInterpolation}} = []
 end
 
-abstract type AbstractParameterNode end
-
-abstract type AbstractDemandNode <: AbstractParameterNode end
-
 """
 In-memory storage of saved mean flows for writing to results.
 
@@ -307,6 +303,10 @@ In-memory storage of saved instantaneous storages and levels for writing to resu
     t::Float64
 end
 
+abstract type AbstractParameterNode end
+
+abstract type AbstractDemandNode <: AbstractParameterNode end
+
 """
 Caches of current basin properties
 """
diff --git a/core/src/write.jl b/core/src/write.jl
index 39a706d97..bb3ad0472 100644
--- a/core/src/write.jl
+++ b/core/src/write.jl
@@ -276,18 +276,9 @@ function concentration_table(
     ntsteps = length(data.time) - 1
     nbasin = length(data.node_id)
     nsubstance = length(basin.substances)
-    nrows = ntsteps * nbasin * nsubstance
 
     substances = String.(basin.substances)
-    concentration = zeros(nrows)
-
-    idx_row = 0
-    for cvec in saved.flow.saveval
-        for concentration_ in vec(cvec.concentration)
-            idx_row += 1
-            concentration[idx_row] = concentration_
-        end
-    end
+    concentration = FlatVector(saved.flow.saveval, :concentration)
 
     time = repeat(data.time[begin:(end - 1)]; inner = nbasin * nsubstance)
     substance = repeat(substances; inner = nbasin, outer = ntsteps)