Response of soil respiration to changes in soil temperature and water table level in drained and restored peatlands of the southeastern United States.

BACKGROUND: Extensive drainage of peatlands in the southeastern United States coastal plain for the purposes of agriculture and timber harvesting has led to large releases of soil carbon as carbon dioxide (CO2) due to enhanced peat decomposition. Growth in mechanisms that provide financial incentives for reducing emissions from land use and land-use change could increase funding for hydrological restoration that reduces peat CO2 emissions from these ecosystems. Measuring soil respiration and physical drivers across a range of site characteristics and land use histories is valuable for understanding how CO2 emissions from peat decomposition may respond to raising water table levels. We combined measurements of total soil respiration, depth to water table from soil surface, and soil temperature from drained and restored peatlands at three locations in eastern North Carolina and one location in southeastern Virginia to investigate relationships among total soil respiration and physical drivers, and to develop models relating total soil respiration to parameters that can be easily measured and monitored in the field. RESULTS: Total soil respiration increased with deeper water tables and warmer soil temperatures in both drained and hydrologically restored peatlands. Variation in soil respiration was more strongly linked to soil temperature at drained (R2 = 0.57, p < 0.0001) than restored sites (R2 = 0.28, p < 0.0001). CONCLUSIONS: The results suggest that drainage amplifies the impact of warming temperatures on peat decomposition. Proxy measurements for estimation of CO2 emissions from peat decomposition represent a considerable cost reduction compared to direct soil flux measurements for land managers contemplating the potential climate impact of restoring drained peatland sites. Research can help to increase understanding of factors influencing variation in soil respiration in addition to physical variables such as depth to water table and soil temperature.

Optic disk size in ischemic optic neuropathy.

We measured the horizontal diameter, vertical diameter, and area of the optic disk in fellow eyes of patients with unilateral nonarteritic ischemic optic neuropathy and in control eyes without ocular disease. The fellow eyes of patients with anterior ischemic optic neuropathy had a smaller horizontal than vertical disk diameter (P less than .05), a difference not present in controls. Both the horizontal disk diameter and the disk area were significantly smaller in fellow eyes of patients with anterior ischemic optic neuropathy than in controls (P less than .05). There was no statistical difference in the vertical disk diameters between the two groups. Our findings suggest that a small disk area along with a horizontal shortening of the scleral canal can lead to crowding of optic nerve fibers, predisposing to a circulatory compromise of the optic nerve head in non-arteritic anterior ischemic optic neuropathy.

A randomized study of 5-fluorouracil and filtration surgery.

We conducted a randomized study of 26 patients with a poor prognosis undergoing filtration surgery with and without a low dose of 5-fluorouracil. Mean preoperative intraocular pressure (+/- S.E.M.) in the 5-fluorouracil group (n = 14) was 38.4 +/- 3.08 mm Hg; in the control group (n = 12) it was 41.2 +/- 5.0 mm Hg. Mean postoperative intraocular pressure (+/- S.E.M.) at six to 18 months was 14.4 +/- 1.4 mm Hg in the 5-fluorouracil group and 30.7 +/- 3.9 mm Hg in the control group (P less than .01). Of 14 patients in the 5-fluorouracil group, 12 had a successful outcome at 12 months. Of 12 patients in the control group, three had a successful outcome during this same interval.

A prospective, randomized study of 5-fluorouracil and filtration surgery.

Our study shows that use of a small dose of subconjunctival 5-FU provides significantly lower postoperative intraocular pressure than does no antimetabolite treatment. Morphology of the postoperative blebs suggests that increased filtration results in lower intraocular pressure in the 5-FU group. Corneal epithelial defects were as common with a low dose as with higher doses previously described.

Secondary angle-closure glaucoma after central retinal vein occlusion.

A 65-year-old man developed unilateral nonrubeotic secondary angle-closure glaucoma after central retinal vein occlusion. Therapy was nonsurgical and included medical control of the intraocular pressure. The anterior chamber eventually deepened and panretinal photocoagulation was later necessary because of developing rubeosis iridis and neovascularization of the optic disk. Secondary nonrubeotic angle-closure glaucoma from central retinal vein occlusion must be distinguished from rubeotic glaucoma or pupillary-block glaucoma so that inappropriate medical or surgical treatment can be avoided.

Stromal keratitis complicating anterior membrane dystrophy.

Recurrent erosion of the cornea has been well documented in patients with nontraumatic anterior membrane dystrophies of various types. We examined five patients who, in addition to an erosion, developed stromal keratitis. Three of these patients were subjected to a complete microbiologic workup, but the lesions were all sterile. The lesions healed with conservative treatment of patching and, in some cases, a soft contact lens. Stromal keratitis should be recognized as a complication of the non-traumatic recurrent erosion syndrome, which in turn is frequently associated with anterior membrane dystrophy. The finding of such anterior membrane changes in either eye will lead to the correct diagnosis and treatment of the affected eye.

Photic maculopathy secondary to short-circuiting of a high-tension electric current.

A 21-year-old man was exposed accidentally to the flash of a high-tension short circuit. He subsequently developed a yellow-gray foveolar lesion with mild central visual loss. Fluorescein angiography demonstrated the area of retinal pigment epithelial disruption and was used to follow its evolution over eight months. The energy level at the retina was estimated at 0.87 Joules/cm2, insufficient to create a thermal burn. Therefore, although the patient suffered thermal facial burns, the foveolar lesion represents a photochemical injury to the retinal pigment epithelium and, hence, is similar to solar retinopathy, eclipse blindness, and arc-welder's retinopathy.

Choroidal vascular changes in toxemia of pregnancy.

Twenty-seven patients with toxemia of pregnancy were examined during a postpartum period of two days to eight months. Five of these manifested abnormal photographic and angiographic findings including disk and retinal edema, retinal striae, deep retinal yellow-white focal lesions, choroidal nonfilling, leakage of dye from the optic disk and deep retinal lesions, and retinal pigment epithelial window defects. The location and configuration of the leakage correlated with the defects seen on color photography. The normal retinal, and predominantly abnormal choroidal vascular patterns provide evidence implicating choroidal vascular insufficiency as the primary basis for secondary retinal detachments seen in toxemia of pregnancy.

Cataracts and macular degeneration.

The intraocular lens restores general vision and some degree of independence and mobility to patients with dense cataracts and macular degeneration. The patient, however, must be repeatedly warned that fine central vision, particularly reading, will not be possible after the surgery. An aphakic spectacle leaves such patients a narrow band of vision when superimposed over the macular lesion, and contact lenses are too small for the patient to manage insertion without help.

Thyroid ocular myopathy.

Based upon the ultrasonographic evidence of extraocular muscle abnormalities in all patients with orbitopathy and proven thyroid disease, we conclude that the basic abnormality of thyroid orbitopathy is a panmyositis and that all of the classes described by Werner are expressions of different degrees and manifestations of the same pathologic process. This thesis is supported by presentation of cases of varying severity who have in common extraocular muscle abnormalities. We believe that the process we describe acceptably explains all of the eye signs of this common orbitopathy.