Allochthonous material

Since 1916 the sedimentation rate, Region III of Figure 3, has averaged 644 g m-2 yr-1 or 0.3 cm yr 1 or about 5 times the pre-cultural rate. The diversion of the Cedar River (average flow of 20 m3 s 1 into the lake in 1916 provided the water necessary to operate the ship and canal locks and contributes an estimated 4-5 x 107 kg-yr-1 of allochthonous material, Crecelius [7]. This riverine sediment input would contribute to the greater... 

On the other hand, a permanent supply of ferric oxides to the sediments is provided by sedimentation of allochthonous material. It is unknown to what extent these oxides are reactive with respect to sulfide or whether a predigestion of ferric oxides by bacteria is needed. Various studies indicate that 50% of freshwater sediment iron exists as iron oxide and 20% of the iron is reactive (72). Future studies should be directed to a better understanding of the existence of reactive iron. 

The maximum value of HON/AON increases in systems with allochthonous carbon inputs. The maximum potential is related directly to the allochthonous organic matter input that is respired in the system (Alloch. Resp.). Additionally, the increased HON will depend on the relative growth efficiency of heterotrophic bacteria on allochthonous material (BGEa och) and the C N ratio of allochthonous material (C Nalloc]l), such that... 

Although the data are scarce, the values for lakes are relatively close to the range and average value predicted based on organic C loading. Further, the relatively low HON in Lake Zurich might be expected based on the high primary productivity in this lake and the restricted input of allochthonous material to much of Lake Zurich (Weilenmann et al., 1989). 

Estuaries are in many cases considered to be net heterotrophic as a result of an excess loading of allochthonous materials to the system. 

The study shows the utility of clay studies to karst hydrology. These data show that suspended sediment discharged from a karst aquifer can be derived from erosion of soil tens of kilometers away from the recharge zone of the aquifer. The data also show that other clearly allochthonous material, such as wood and (probably man-made) fibers travel through the aquifer and are discharged at the springs. 

The division into laterite and ferricrete used in this chapter represents a useful process-based distinction, but the practicality of determining whether mineral components of a profile are allochthonous or autochthonous is problematic because many lateritic weathering profiles are subsequently modified by the introduction of allochthonous materials. Conversely, once formed, ferricretes can be subject to weathering processes in situ and evolve toward more lateritic-type profiles. Nevertheless, the distinction between dominantly autochthonous weathering profiles or allochthonous alteration profiles is an important one because it places constraints upon the processes operating during duricrust evolution, and also upon contemporaneous climatic and geomorphological conditions. 

Allochthonous material (clay, minerals, etc.), including Si02 from diatoms. 

In Lake Michigan (31), diatoms appear to play an important role in the sedimentation of Cu and Zn. In Lake Windermere (32), the influence of allochthonous material may be more important. A recent study of Lake Windermere (33) indicated a Zn P ratio of 0.03 from the regression analysis of dissolved concentrations during a diatom bloom. Mountain Lake (34) is a small acidic lake. 

The contribution of allochthonous organic matter to lake sediment humic substances is variable. In this chapter, we did not discuss in depth the contribution of allochthonous materials, such as soil organic matter, to sedimentary humic substances. However, it is important in the study of lake humic substances to determine how much authochthonous or allochthonous organic matter contributes to the formation of lake humic substances. Therefore, a method must be established for estimating the degree of contribution of authochthonous or allochthonous organic matter to lake humic substances. 

Hiriart-Baer, V.R, Diep, N., and Smith, R.E.H. (2008). Dissolved organic matter in the Great Lakes Role and nature of allochthonous material. J. Great Lakes Res., 34,383-394. 

---