Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)




Sand bars and beaches of the Mississippi (MR) and Wild Rice (WRR) Rivers, Minnesota, were sampled to allow determination of sand texture, capillarity, pore space, organic content, temperature, chemistry (pH, Og, CO3 and HCO3 alkalinity, total hardness, Ca, Mg, PO^, NH3-N, and NO2-N) of interstitial, water, and composition and concentration of psammo-organ!sms, all in relation to current influences, distance above and below waterline, and depth into the sand.

Minimum and maximum values for capillary rise were 36-80 mm in the MR and 118-191 mm in the WRR; organic content was 21?,4 mg/lOcc sand for the MR and 377.1 mg/lOcc sand for the WRR; and pore space comprised 22- 25$, and 35-37% of the total sand volume for the MR and WRR, respectively. Submerged sand was frequently moved by stream currents.

Oxygen was absent from water 6-9 cm deep in exposed sand of both streams and in submerged sand of the WRR, but occasionally occurred in submerged sand in the MR (maximum 4.4mgl); pH decreased progressively from stream to submerged to exposed sand (exemplified as follows for the MR, 8.25, 7.15, and 6.95, respectively; and for the WRR by 7*6, 6.7, and 6.4, respectively) as decomposition became mere localized. Carbonate alkalinity was not observed in interstitial water of either river. Bicarbonate alkalinity (range 114-252 mgl for the MR and 3 58-552 mgl for the WRR), total hardness (142-274 mgl MR and 189-693 mgl WRR), calcium (54-199 mgl MR and 99-395 mgl WRR), and magnesium (46-132 mgl MR and 24-287 mgl WRR) increased in the same order as pH, seemingly because of ground water seepage, decomposition, and evaporation. Ammonia-nitrogen (0.0-5.0 mgl) and ortho-phosphate (0.0-5.84 mgl) were contributed to the psammon of the WRR by local surface drainage. Lower levels (0.0-2.0 mgl and 0.0-2.6 mgl, respectively) occurred in MR sand.

Composition and concentration of psammo-organisms were related to distance above and below waterline and to depth in the sand. Three hundred twenty-six (326) kinds of organisms were found in 700 samples. Potamopsammon organisms in descending numerical order were: diatoms (maximum number 2,181,824/cc sand MR and 441,4?0/cc sand WRR), blue- green algae (62,038 MR, 210,624 WRR), green algae (19,757 MR, 4,186 WRR), testaceous rhizopods (4,408 MR, 1,152 WRR), euglenophytes (2,480 MR, 2,160 WRR), rotifers (452 MR, 32 WRR), nematodes (216 MR, 184 WRR), tardigrades (188 MR, 8 WRR), dinoflagellates (112 MR, 0 WRR), oli- gochaetes (76 MR, 12 WRR), gastrotrichs (72 MR, 0 WRR), ciliates (56 MR, 4 WRR), dipteran larvae (56 MR, 30 WRR), ostracods (40 MR, 16 WRR), and hydrachnid larvae (40 MR, 0 WRR),

Potamopsammon organisms were most numerous in stable submerged sand. They were next most abundant in exposed sand within 70 cm of the waterline, newly formed sand bars under water, eroded portions of submerged sand, exposed sand 70+ cm above the waterline, and at the waterline, in that order.

The major portion of the population was usually located in the upper two centimeter's of stable sand, but organisms penetrated to a depth of six centimeters. Concentration at any point or depth in submerged sand was subject to depletion or augmentation by current action. Organisms were most numerous at a depth of three or more centimeters in newly- formed submerged bars, partly from burial of established surface sand populations, and partly from loss of organisms from newly deposited sand.

Potamopsamnion as exemplified by these study areas differs from lake psammon in the following respects: oxygen was absent in the interstitial water of exposed sand, a black layer was absent from the sand, fewer species of rotifers were present, harpactacoid copepods were absent, a more diverse blue-green algal flora, was noted, algae were found in greater abundance, and organisms were found to exist at greater depths in potamopsammon than in lake psammon.